Talmud - Shabbat 48a שבת מ״ח א׳

causing heat to rise, i.e., heating food that is not actually insulated in it, but merely resting upon it, the residue of olives causes heat to rise. Therefore, it is prohibited even to place cooked food upon it. However, the residue of sesame does not cause heat to rise to that extent. Therefore, it is permitted to place food upon it.

The Gemara relates an anecdote somewhat relevant to the previous discussion: Rabba and Rabbi Zeira happened to come to the house of the Exilarch on Shabbat, and saw this servant who placed a jug [kuza] of cold water on the mouth of a kettle filled with hot water. Rabba rebuked him for having acted contrary to the halakha. Rabbi Zeira said to Rabba: How is this case different from placing an urn on top of another urn, which is permitted on Shabbat? Rabba said to him: There, when he places one urn on top of another urn, he merely preserves the heat in the upper urn; therefore, it is permitted. Here, in the case where he places the jug of cold water on the mouth of a kettle, he is generating heat in the water in the upper vessel; therefore, it is prohibited.

The Gemara continues: Rabba then saw that same servant spread a kerchief [dastodar] over a vat of water and place a cup used to draw water from the vat, on the kerchief. Once again, Rabba rebuked him for having acted improperly. Rabbi Zeira said to him: Why did you rebuke him? Rabba said to him: Now, see what will happen. Ultimately, he saw that the servant was squeezing out the water that was absorbed by the kerchief, thereby violating a Torah prohibition. Nevertheless, Rabbi Zeira said to him: How is this case different from that of a cloth [parvanka], which one is permitted to spread over a vat even on Shabbat? Rabba said to him: There is a distinction between the two cases: There, in the case of the cloth, he is not particular about it; even if it gets wet, he will not come to squeeze it dry. Here, with regard to the kerchief, he is particular about it, and he will wring it so that it will not remain wet.

We learned in the mishna: And one may neither insulate a pot in straw, nor in the residue of grapes that were pressed for their juice, nor in soft material. Rav Adda bar Mattana raised a dilemma before Abaye: With regard to swatches of soft material in which he insulated a pot, what is the halakha with regard to moving that material on Shabbat? Ordinarily, swatches of materials of that kind are set-aside because they have no use. Therefore, moving them on Shabbat is prohibited. Do we say that since they are now being used to insulate a pot, they assume the legal status of a utensil, which may be moved on Shabbat?

Abaye said to him: Just because he does not now have a basket of straw in which to insulate his food, does he stand up and renounce his basket of soft material? Obviously, he would have preferred to insulate his food in straw, as it is less expensive. The only reason that he used that material was because there was no straw available at the time. However, he does not want the swatches of material to be used for any other purpose, lest it be ruined. Therefore, it remains set-aside.

The Gemara asks: Let us say that the following baraita supports him: One may insulate a pot of food on Friday afternoon in woolen fleece, in combed wool, in tabs of wool dyed purple, and in swatches of soft material; however, he may not move them. Apparently, this is in accordance with the opinion of Abaye.

The Gemara rejects this proof: If that is the reason, there is no conclusive argument, as it is saying in the baraita as follows: If, however, he did not insulate a pot in them, he may not move them on Shabbat. In that case, they remain earmarked for their own purpose and are therefore set-aside [muktze].

The Gemara questions this last assertion: If so, what is the reason to say that? Obviously, those materials are set-aside. The Gemara explains: Lest you say that all these materials are suitable for one to sit on them, and, consequently, their legal status is that of utensils, which may be moved. Therefore, the baraita teaches us that this is not so, and they may not be moved due to the prohibition of set-aside.

The Gemara relates that Rav Ḥisda permitted returning stuffing to the pillow from which it had fallen on Shabbat. Rav Ḥanan bar Ḥisda raised an objection to the opinion of Rav Ḥisda from a baraita: One may untie the neck opening of a shirt on Shabbat if it had been tied by the launderer; however, one may not open a new neck opening for the first time on Shabbat. And one may not place soft material into a pillow or into a cushion on a Festival, and, needless to say, one may not do so on Shabbat. This baraita contradicts the ruling issued by Rav Ḥisda.

The Gemara answers: This is not difficult. This, the baraita is referring to new pillows, whereas that, the statement of Rav Ḥisda is referring to old pillows. Stuffing a pillow for the first time on Shabbat is prohibited because by so doing one fashions a new utensil. However, if the stuffing fell out of the pillow, refilling the pillow is permitted even on Shabbat.

The Gemara notes: That opinion was also taught in a baraita: One may not place soft material as stuffing into a pillow or into a cushion on a Festival, and needless to say one may not do so on Shabbat. However, if the stuffing fell out, it may be replaced even on Shabbat, and needless to say that doing so is permitted on a Festival.

Having raised the issue of opening a collar, the Gemara cites that Rav Yehuda said that Rav said: One who opens a new neck opening in a shirt on Shabbat, by cutting through the fabric and threads that kept it closed, is liable to bring a sin-offering. By creating the opening, he renders the shirt fit to wear, thereby fashioning a utensil on Shabbat.

Rav Kahana strongly objects to this:

Traduction : The William Davidson digital edition of the Koren Noé Talmud, with commentary by Rabbi Adin Even-Israel Steinsaltz.

Shabbat 48a examines which insulating residues retain versus generate heat, and shares a rabbinic anecdote debating proper use of cloths near hot water on Shabbat.