Friday, May 31, 2013

Moving a Fan on Shabbos

Question:
Can one move a fan on Shabbos?

Discussion:
A fan is considered, by many Poskim, to be a kli shemilachto l'issur (an object whose primary use is prohibited on Shabbos); therefore it can be moved if its' place is needed or if you are using it for a permitted usage. This means that if the fan is blowing on a person and he no longer wants it to be blowing on him he can move the fan. This falls under the category of needing its' place because when the fan is blowing in his direction it is stopping him from using that spot comfortably.

It is also permissible to move the fan so that it is blowing on you as well since this is considered using it in a permissible way. Rav Moshe zt"l however, has an interesting view on this matter (O.C. 5:23, 22:22). He holds that a fan is actually a kli shemilachto l'heter (an object that has a permitted usage) because the action of the fan is not prohibited (i.e. the spinning of the blades), even though the cause of the spinning (the electricity) is something prohibited. So, according to Rav Moshe zt"l one would be allowed to move the fan for any reason. Care must be taken to make sure it is not unplugged. This is only if the fan is functioning; if the fan is off then it should not be moved at all unless the spot the fan is occupying is needed.

Another question is can one make the fan oscillate assuming that one does not have to press a button or use electricity to do so? There is a difference of opinions regarding this. Rav Auerbach zt"l says that it is permissible to do so even if a small amount of electricity since it is undetectable to human senses (Shulchan Shlomo 308:34). Rav Elyashiv zt"l says that it would be prohibited unless no electricity was used at all (Meor Hashabbos 14:117)           

Summary:
One is permitted to move a fan that is functioning on Shabbos. However, there is a dispute in regards to making the fan oscillate on Shabbos. Rav Elyashiv zt"l says one cannot make it oscillate and Rav Auerbach zt"l says one can make the fan oscillate on Shabbos.     

Friday, May 24, 2013


Question:
Why can't I use electrical appliances on Shabbos?

Discussion:
It is common knowledge that the use of electrical appliances is prohibited on Shabbos however, the reason for the prohibition is not so clear. We will put forth some of the reasons for the prohibition.

Molid - Creating a new entity:
One reason given by the poskim for the prohibition of using electrical appliances is the concept of Molid (creating something new). By allowing an electrical current to run through an appliance you are effectively creating a (new) usable appliance, which is prohibited on Shabbos. This is the opinion of the Bais Yitzchak (2:31). In a similar vein, Rav S.Z. Auerbach writes that the prohibition is the creation of sparks, which are generated by the electrical current (Minchas Shlomo 1:10:7).

Makeh B'Patish - Finishing touch:
The opinion of the Tzitz Eliezer (6:6) and the Minchas Yitzchak  (3:41) is that when an electric current is introduced in the appliance you are effectively putting the finishing touch on an object that until now was not complete since it did not have a use.

Boneh - Building:
The Chazon Ish (Shabbos 50:9) was of the opinion that when a circuit is completed it is a form of the Av Melacha of Boneh.

Bishul - Cooking:
An additional reason given by the Chazon Ish for this prohibition is when the current passes through the wire it causes the temperature of the wire to rise above Yad Soledes Bo (110 degrees F). This is under the melacha of Bishul.

Summary:
It is accepted that the use of electrical appliances is prohibited on Shabbos although the reason is a cause of considerable debate. One outgrowth of this debate is the possible permissibility of having a non-Jew turn on or off an appliance. A rav should be consulted if the need for this arises.

Sunday, May 12, 2013

Placing trees in homes on Shavous.


Question:
What is the custom regarding placing trees and grasses in our homes on Shavous?

Discussion:
There are really two separate customs that people have; one is to place flowers and other plants in our homes and shuls. This is to remind us of the simcha of Matan Torah when Hashem caused grass and plants to grow on Har Sinai (Rema 494:3). There is another custom of placing trees in our homes. This is based on the Mishna (Rosh Hashanah 16a)that tells us that on Shavous we are judged on the fruit trees, through placing them in our homes we will have them in mind while we are davening (M.B. 494:10).

However, the Chayei Adam writes (131:13) that the Gr”a was of the opinion that this custom should be discontinued since it is now a non-Jewish custom to place trees in their homes on their holidays. The Aruch Hashulchan (494:6) writes that both customs were removed in earlier generations and therefore there is no longer a custom to place trees or flowers in our homes; this is the opinion of Rav Moshe zt”l as well (Iggros Moshe Y.D 4:11:5).

The opinion of the Steipler Gaon (Orchos Rabbenu vol. 2 pg.99), Rav Aurebach (Shalmei Moad pg. 459), and Rav Elyashiv zt”l (Chag B’Chag 8:24) was that it is not a non-Jewish custom to spread grasses and therefore one may do so on Shavous. Interestingly, although the Steipler said that it is not a non-Jewish custom it is quoted in his name that one should not spread out grasses in Eretz Yisrael (Kovetz Ohr Yisrael 20:136). 

Wednesday, May 8, 2013

Tefillahs Haderech Part II


Question:
What are some Halachos of Tefillahs Haderech (part II)?

Discussion:
The proper time to say Tefillahs Haderech is once the trip has begun. Practically, one should wait until he is more than 70 amos past the last house of the city (M.B. 110:29). Ideally, it should be said during the first “parsa” of travel – a parsa is 8,000 amos - (Rema 110:7). If one stopped overnight, the tefillah can be said even before he leaves the city that he stopped at (M.B. 110:29). Once a person is within a parsa of his destination, he should not recite the concluding bracha.

If one is traveling less than a parsa, he should not conclude the tefillah with the bracha. However, if there is danger within a parsa of the city, the tefillah is recited while traveling within that parsa.
All these Halachos apply to a ship as well as traveling on land. It would seem that if a person goes on a cruise he should recite Tefillahs Haderech each morning of the cruise.

When travelling by plane one should recite the tefillah while the plane is taking off. If one had to travel outside the city to reach the airport then the Tefillah should be recited when he leaves the city. It does not need to be repeated when the plane takes off. So for example when one leaves Yerushalayim he should recite Tefillahs Haderech and then does not need to say it again when he takes off from Tel Aviv.  

Friday, May 3, 2013

What are some Halachos of Tefillahs Haderech (part I)?



Question:
What are some Halachos of Tefillahs Haderech (part I)?

Discussion:
The custom is to say the tefillah in plural from even when travelling alone since this will help the tefillah have more of an affect (M.B. 110:19). The Mishna Berura also writes that a person should make sure to travel with food since when travelling it is possible for an accident to happen and he might find himself without kosher food.  Additionally, one should make sure to travel with Tallis and Teffilin even if he is planning to return the same day since it is possible that he will be delayed and miss the mitzvah. This is true even if he would be able to borrow someone’s Teffilin (M.B. 110:20).

One should stop travelling while saying Tefillahs Haderech; however, if this will cause him to delay and he will not be able to concentrate it may be said while traveling (S.A. 110:4). When traveling by plane, bus, or train and it is possible to stand while saying Tefillahs Haderech, one should do so (Aruch Hashulchan 110:11).  
The obligation of this tefillah is once a day while travelling. Therefore, if a person is traveling for two days and stops overnight, he should say this tefillah twice; this is true even if he resumes traveling while it is still night. If the stop was a short one and he continued traveling, a new tefillah is not made. If one is traveling the entire day and night, he should repeat the tefillah without the concluding bracha. Therefore, if one is on a cruise he should make sure to say Tefillahs Haderech each morning without the concluding bracha (Eishay Yisrael 50:4:13). 

If, upon reaching his destination, he changes his mind and wants to continue traveling, he should say Tefillahs Haderech again (S.A. 110:5).  

The bracha should ideally be connected to another bracha so if possible one should first go to the bathroom, make an Asher Yotzar, and then say tefillah Haderech. Another option would be to eat something, make a bracha achrona, and then say Tefillahs Haderech. If this is not possible, Tefillahs Haderech should be said anyway (M.B. 110:28).

Thursday, April 18, 2013


Question:
Can I make the “Berchas Elanos” after Nissan?

Discussion:
The Gemara in Brachos (43) tells us that “one who goes out during Nissan and sees trees that have begun to bud makes a bracha…” The Mishna Berura (226:1) writes that this bracha does not have to be said specifically in the month of Nissan but rather whenever the first time that you see a tree with buds on it you can make the bracha. The Mishna Berura comments further that this bracha is only to be made on a fruit bearing  tree.

This bracha should not be said on a spice tree since spices are not considered fruit (Maaseh Chemed Ch. 2 note 79).

The definition of a tree for this halacha is something that survives from year to year and lasts for at least three years (Chazon Ish).

If one did make a bracha on a non-fruit bearing tree he should not repeat the bracha since there are opinions that you can make the bracha on such a tree (Shevet Halevi 6:53:4). Additionally, he writes that if one made the bracha without even seeing the tree he should not repeat the bracha when he does see it.
It is preferable to make a bracha on two trees that are growing near each other rather than on one tree that is alone since the bracha was written in plural. However, if this is not possible then the bracha can be said on a single tree (Kitzos Hashulchan 66:18).     

Wednesday, April 10, 2013


Question:
Is one permitted to clap or whistle on Shabbos?
Discussion:
There is a rabbinic prohibition of producing sounds on Shabbos using an instrument. The reason for this is the rabbis were concerned that one may come to adjust the instrument and thereby perform the melacha of Makeh Bepatish (putting a finishing touch on an object).  The Rema (338:1) writes that this prohibition includes any object whose primary purpose is to create sound - not just musical instruments. He therefore writes that using a doorknocker on Shabbos would be prohibited (in extenuating circumstances it may be permitted see B.H. s.v. since).
Likewise it is forbidden to produce musical sounds using objects that are not intended to create sound, such as put covers, while singing (338:1 M.B.1; M.B. 339:3:9). It would be permitted to use these objects to make a sound that is not musical in nature such as to get someone’s attention.
Clapping:
In the times of Chazal singing and clapping often was accompanied by musical instruments. Chazal prohibited clapping while singing to ensure that musical instruments would not be used and perhaps adjusted. One can certainly clap in order to get someone’s attention or to wake someone up (Nishmas Shabbos 3:464). There are poskim that permitted clapping while singing for various reasons which are beyond the scope of this email (see Aruch Hashulchan 339:9; Iggros Moshe O.C. 2:100). One option which would be permitted according to all would be to clap in an unusual manner such as clapping the back of one hand on to the palm of the other (S.A. 339:3). Some poskim permit clapping while singing zimeros since this enhances the mitzvah (Nishmas Shabbos 3:463).
Whistling:
One is permitted to whistle on Shabbos as Chazal did not enact any ordinance regarding making noise with one’s mouth. This includes whistling made by putting one’s fingers in his mouth as well 338:1).
Dancing:
Dancing is also prohibited on Shabbos (339:3) however, the leniencies that apply to clapping apply to dancing as well.  

Thursday, March 14, 2013


Question:
What are some of the laws of Heseiba, Reclining?
Discussion:
On the night of the Seder, we are supposed to act as if we ourselves were taken out of Egypt. One of the ways we do this is by eating in the way of free men – which is to recline while eating (Shulchan Aruch HaRav 472:7).
One is required to recline at the following points in the Seder, while eating the Matzah, (this includes koraich and Afikomen) and while drinking each of the Four Cups. There is a discussion regarding reclining while eating the Karpas, one should follow his custom. If he has no specific custom he should recline since the dipping is to show freedom (Halachos of Pesach pg. 247)
The Opinion of the Ra’avyah:
There is an opinion that holds that since it is no longer the custom of nobility to recline it is no longer a sign of a free man is in unnecessary at the Seder. However, we generally do not follow this view since most poskim hold that it is still a sign of freedom.  Therefore, if one did not recline at the appropriate places he must redo the mitzvah. However, if one did not recline while drinking the first Cup he should not drink a new Cup.
Women:
The general custom is that women do not recline since it was never the custom of women to do so (even when it was normal for people to recline). Additionally, the opinion of the Ra’avyah is that no one is required to recline therefore the custom developed that women do not recline (M.B. 472:12).  

Wednesday, March 6, 2013


Question:
What are the laws of the 4 Cups?
Discussion:
 We drink four cups of wine at the Seder because wine is the drink of a “free man” (Pesachim 117b). Each of these cups is drunk after completing four mitzvos at the Seder. They are 1) Kiddush 2) reciting the Hagaddah 3) Bentching 4) Hallel. These cups must be drunk at the right place therefore if one drinks four cups one after the other he has not fulfilled his obligation (M.B. 472:26).
How much must I drink?
The cup must contain a “rivis” of wine (the exact meassurments will be the topic of a subsequent email.) and it is preferable to drink the entire cup one must drink at least a majority of the cup (M.B. 472:30). Additionally, it must be dunk in a specific amount of time there is some debate among the poskim as to what the exact time is the opinions range from one (or two swallows with minimal time in between) to nine minutes (M.B. 170:8; 472:34). If it took a person longer than nine minutes to drink rov rivis (most of a rivis) then a new cup should be drunk with a new bracha ( Shar Hatzyun 472:47).
Can I use Grape Juice?
There are two aspects in the mitzvah of the Four Cups, one is the act of drinking it and the other is the feeling of “freedom” that it represents. In order to fulfill both aspects one should use wine for the four cups even if it causes him some discomfort (O.C. 472:10). The Gemara says that the wine must have the appearance and taste of wine this means that grape juice should preferably not be used (Shulchan Aruch HaRav 742:27). One is permitted to mix the wine with grape juice provided that the wine taste is not lost. If one gets sick from drinking wine then he should use grape juice (M.B. 472:35).
Women and Children:
Women have an equal obligation in drinking the Four Cups as men do and therefore all the halachos that apply to a man are applicable to a woman as well. Like any other mitzvah, parents are obligated to train their children in the mitzvah when they reach the age that they can understand the mitzvah. The Cups should be drunk in the proper place and not all at once.  

Thursday, February 28, 2013


Question:
What is the mitzvah of “Retelling the story of our exodus from Egypt”?

Discussion:
There is a unique mitzvah on the night of the Seder, which is the retelling of our freedom from Egypt. This is a Torah commandment that can only be fulfilled on the night of the Seder. Although the Torah uses the terms of a father telling the story to his son (Shemos 13:8) we know that everyone is obligated to retell the story.

Are women obligated in this mitzvah?
Women are obligated in this mitzvah however, there is some discussion if it is a Biblical obligation or a Rabbinic one. Either way they should make sure to participate in all the mitzvos of the night. The absolute minimum that a woman (or a man) must be part of is from “Raban Gamliel…” until the second cup has been drunk. There are some poskim that say women should also be present for the “Ten Plagues” as well.

However, it should be noted that women are obligated in all the mitzvos of the night and are therefore required to drink the four cups at their proper place in the Hagaddah as well as eating the matzo and marror (Beur Halacha 472:8). 

Children
There is a mitzvah of chinuch in all the mitzvos of the night. Therefore, once a child can understand the story he or she should participate in the Seder. Usually, this begins between the ages of 5 or 6 but it can vary depending on the child (Shulchan Aruch HaRav 472:25).

It is important for parents to ensure that their children sleep during the day so that they can stay up at night to hear the Hagaddah. They should not be put to sleep until after the Maggid part of the Seder is done. Obviously, as the children get older they should be encouraged to stay until the end of the Hagaddah. The Gemara relates that Rabbi Akiva used to leave the Bais Medrash to ensure that the children would take a nap during the day (Pesachim 109a). 

Thursday, February 21, 2013


Question:
What are some halachos of Mattanos L’Evyonim?

Discussion:
Note: Many of these halachos come from the sefer Kovetz Halachos al Purim unless otherwise noted.

The minimum amount of money one must give is one dollar to each poor person (Kovetz Halachos al Purim). Some say that one should give enough money to purchase a small meal (e.g. a bagel and a coffee).
One can fulfill this mitzvah by giving a check- providing that there is a way to get cash for it (someone will cash it for him, the bank is open or a store will accept it etc. – Halichos Shlomo 19:23).

Women are obligated in this mitzvah. A married woman may fulfill her obligation with her husband’s donation (Aruch Hashulchan 694:2 see also 695:18). Some poskim say that a married woman should give her own Mattanos L’Evyonim.  A son that is supported by his father is obligated in this mitzvah as well. However, the father may pay for it using his own funds.

One is not obligated to train his children in this mitzvah.

There is a dispute as to whether one should give a large donation to two poor people, thereby giving them a lot of simcha, or giving many people a smaller amount. The Bach (§675) says it is better to give less to more people. Rav Elyashiv shlita is quoted as saying one should give a large amount to less people.

Money which is already designated for tzeddakah may not be used for Mattanos L’Evyonim. Similarly one cannot use maser money.

Money may be given to a tzeddakah collector before Purim providing that he will distribute the money on Purim itself.

The Halacha of “we give to any one that asks for tzeddakah on Purim” only applies to individual people. This does not apply to people collecting for institutions. 

Thursday, February 14, 2013


Question:
What are some of the laws of Mishloach Manos?
Discussion:

Note: These Halachos come from the Mishna Berura 695:4 unless otherwise indicated.

The minimum one must send is two food items to one person. Drinks are included in the food category regarding this mitzvah. Seltzer is not considered a food item since it is similar to water (Kovetz Halachos).
One cannot fulfill his obligation by sending anything besides food. It is not necessary to ensure that they are separate brachos (Kovetz Halachos).

It is best to use a messenger (shliach) to deliver the mishloach manos if one does not use a shliach it is questionable if he fulfills his obligation (Binyan Tzion 44). The shliach can be a minor or a non-Jew (Silmas Chaim 276). The food has to be ready to eat however there is an opinion that if the food is ready to be cooked that is considered ready to eat.

The mitzvah of mishloach manos can only be done on Purim day, if it is given at night one needs to send another one in the morning. However, if the package will arrive on the day of Purim he has fulfilled his obligation.

Women are obligated in the mitzvah of mishloach manos; the opinion of the Magen Avrohom is that a married woman fulfills her obligation with her husband. The Mishna Berura ends off saying that a woman should send her own mishloach manos.  The Rema writes that a woman should only send to a woman and a man to a man.

Many poskim are of the opinion that the reason why we send mishloach manos is to increase the feelings of love and friendship in the community, therefore if one sends an anonymous mishloach manos he has not fulfilled the mitzvah (Kovetz Halachos).  

Thursday, February 7, 2013


Question:
Can one fulfill his obligation of reading the Megillah over the phone?

Discussion: 
There are really three variations of this question. The first is can one hear the Megillah over the phone. The second is can one listen to the Megillah through a microphone. The third is can one use a hearing aid and fulfill his obligation of reading the Megillah.

According to Rav Shlomo Zalman Auerbach zt"l one is does not fulfill his obligation if he hears the Megillah through a speaker system. This is because the sound one hears is not the actual voice, rather, an electronic replication of the person's voice (Minchas Shlomo 1:9). The same would be true if he heard it over a telephone. If a person is deaf or is hard of hearing and has a hearing aid, he should ask a rav what the proper course of action is.  

Rav Moshe zt"l agrees that one should not use a microphone or hear the Megillah over the phone. However, his reason is different then Rav Auerbach's reason (Iggros Moshe O.C. 2:108).

According to Rav Shmuel Kaminetsky, (Kovetz Halachos pg. 84) a person should take out his hearing aids to listen to the Megillah. The reason for this is since the main sound he hears is coming through the hearing aid he cannot fulfill his obligation while wearing them.           

Summary: 
One needs to hear the sound directly from the one reading the Megillah. Therefore, one cannot hear the Megillah over the phone or through a microphone. According to Rav Kaminetsky zt"l, a person with a hearing aid should take out his hearing aid and stand as close as he can to the chazzan. If one cannot hear at all without his hearing aid a rav should be consulted.   

Sunday, February 3, 2013


Question:
Why do we read four special parshios during the month of Adar?

Discussion: 
The Mishna Berura (685:10) explains that we read these parshios to commemorate different events that took place. The first parsha that we read is Shekalim. The reason for this is that in the times of the Bais Hamikdash there were sacrifices that were brought on behalf of the entire nation. The money for these sacrifices was collected every year during Adar. Therefore, we read the parsha that talk about donating to the Mishkan to commemorate the obligation to give money for these sacrifices.

Parshas Zachor is to fulfill the mitzvah of destroying Amalek. We read it the week before Purim to join the two episodes of Amalek. Since Parshas Zachor is a torah obligation, one should be careful to hear every word that is read. If a person missed a word he should ask a Rav what to do because there is a Machlokes in this matter.

Parshas Para is read to commemorate the first Parah Adoma that was brought in the desert. We read it before the month of Nissan since in the times of the Bais Hamikdash it was important to be spiritually pure so that the Korban Pesach can be brought. Parshas Hachodesh is to sanctify the month of Nissan. 

One does not have to read Shnayim Mikrah on these extra Parshas that we read (Terumas Hadeshen). However, if a person is accustomed to reading the Haftorah before Shabbos then he should read the special Haftorah for these Parshas.

A Woman’s obligation in Hearing the Four Parshas
Women are not obligated to hear any of these special parshios (even Parshas Zachor). If a woman wants to come to shul, she is certainly welcome to. One should not make a special reading for women unless there is also a minyan of men that have not fulfilled their obligation.


Sunday, January 27, 2013


Question:
Is one obligated to wear a Yarmulka (head covering) at work?

Note: We are only discussing the issue of wearing a yarmulka in the workplace. There are other issues that come up such as making a bracha or learning torah that we are not going to discuss.

Discussion:
Wearing a Yarmulka is a universally accepted custom. The source for this custom is based on the Gemara in Shabbos (156) that tells us “cover your head so that you will have the fear of Heaven”. The T”Z writes that in addition to the reason the Gemara brings, there is another reason we cover our heads. In his time the gentiles would remove their hats as soon as they entered their house or sat down. If we would do the same we would transgress the prohibition of “Following their Ways.” Based on this it would seem that it is not just a custom but something that is required.  

Wearing a yarmulka at work:
Rav Moshe writes in his Teshuvos (O.C. 4:2) that if a person will stand to lose his job (or won’t get hired) then he is not required to wear a yarmulka. However, one must still wear it when he makes a bracha or eats anything. A rav should be consulted if one is concerned a potential client will not feel comfortable if he wears a yarmulka. 

Wearing a yarmulka in court:
The Aruch Hashulchan writes that one may remove his yarmulka if a judge asks him to do so in the courtroom (2:10). However, one should try his utmost to convince the judge to permit a head covering (Melamed L’hoel 2:56). The following link is to an interesting article about wearing a yarmulka in court. www.jlaw.com/Commentary/yarmulke.html

Summary:
Although the main reason for wearing a yarmulka is based on custom there is the opinion of the T”Z which says that it is, in fact, an obligation. However, there is room for leniencies if it will cause a person to lose his job (or not get it in the first place). However, we must not downplay the significances of this custom that has been universally accepted. 

Sunday, January 20, 2013


Question:
What are some laws of Lechem Mishneh?

Discussion:
The reason why we use two loaves of bread is to remind us of the double portion on the Mann that came down on Friday. This is also the reason why there is a custom to cover the challah on top and on bottom since the Mann came sandwiched between two layers of dew.

Men and women are equally obligated in using Lechem Mishneh at each of the three meals on Shabbos (M.B. 274:1).

Even if the bread has a crack, it is considered complete as long as the bread will not break if it is picked up by the weaker section (M.B. 167:11). If two loaves became attached during the backing process they may be separated from each other and would still be considered complete (Machtzis Hashekel 274:1).
As long as the loaf is not missing more then 1/48th of the entire loaf it is considered complete (Machtzis Hashekel 274:1). However, there are others that say it is no longer considered whole (Aruch Hashulchan 274:5)

If one does not have two complete loaves of bread, he should use one loaf and one piece of bread. If one has no complete loaves then he should make Hamotzie on two pieces of bread (Minchas Yaakov 12). If one has a whole loaf and a whole cake he may use the cake as part of the Lechem Mishneh. In this case he should eat from both the loaf and the cake (Shu”t Daas Moshe 4).  

Friday, January 18, 2013


Question:
Can one be menachem avel  (comfort the mourner) over the phone?
Discussion:
The Rambam writes that there are two aspects of nichum aveillim; the first one is to comfort the mourners in their time of distress over the loss of their relative. This is done by expressing sympathy and consoling them over their loss. The other aspect of the mitzvah is to elevate the nishama of the departed person.
One can fulfill the first aspect of the mitzvah merely by being in the house of mourning even without saying anything (Moed Katan 21b). To fulfill the second aspect of the mitzvah it is necessary to visit the home of the deceased (Shabbos 152a).
Rav Moshe zt”l writes (O.C. 4:40:11) That while it is possible to comfort a mourner over the phone, it is not possible to elevate the soul of the deceased without actually coming to the house of mourning. Additionally, a phone call may not be the most respectful way of comforting the mourner. Therefore, if one can visit the mourner in person he should do so. However, if it is not possible to visit the mourner then a phone call would be the next best option.
Nichum Aveillim on Shabbos
The accepted custom is not to comfort a mourner on Shabbos or Yom Tov (Aruch Hashulchan O.C. 287:3). If one would be unable to be menachem him during the week then it may be done on Shabbos (ibid 1). The Kaf Hachaim (O.C. 287:4) writes that when one is menachem avel on Shabbos he should not say any explicit words of nechama and should keep his visit to a short amount of time.