Talmud - Nedarim 43a נדרים מ״ג א׳

GEMARA: Granted that the person from whom benefit is forbidden may not lend money to the person for whom benefit is forbidden, as he thereby benefits him. However, with regard to the fact that the former may not borrow money from the latter, in what way does he benefit him by borrowing his money? And it could even be said, granted that he may neither borrow money from him nor purchase an item from him, as one benefits in lending money by preserving the value of that money in case the coins deteriorate, and in selling by ridding oneself an item that is difficult to sell. However, with regard to the fact that the person from whom benefit is forbidden may not borrow an item from the person for whom benefit is forbidden, in what way does the lender benefit from him? The borrower returns the same item to the lender.

Rabbi Yosei, son of Rabbi Ḥanina, said: The mishna is referring to a case where they both vowed that benefit from each other is forbidden. Clearly, then, neither of them may lend to the other or borrow from him. Abaye said: It is possible to explain the mishna as it is written, as referring to a case where only one vowed that benefit from the other is forbidden. However, the Sages issued a decree that it is also prohibited for one to borrow from a person for whom benefit from him is forbidden, due to the concern that he might come to lend to him, as reciprocity is common in these matters. And likewise, that is the explanation in all the cases in the mishna; it is prohibited to borrow money, borrow items, and to purchase items from him due to a rabbinic decree, lest he come to benefit him.

MISHNA: One said to another: Lend me your cow. The other person said to him: My cow is not available. The one seeking to borrow the cow responded angrily: Plowing my field with this cow is konam forever. If it was his typical manner to plow the field himself, then it is prohibited for him to plow his field with that cow but it is permitted for every other person. If it is not his typical manner to plow the field himself, and he has others plow for him, it is prohibited for him and for every other person to plow his field with that cow, because his intent was to render benefit from plowing with this cow forbidden.

In the case of one for whom benefit from another is forbidden by vow and who does not have anything to eat, the one from whom benefit is forbidden goes to the shopkeeper and says to him: So-and-so vowed that benefit from me is forbidden for him and I do not know what I will do. After grasping his intent, the shopkeeper gives food to the one for whom benefit is forbidden, and then the shopkeeper comes and takes payment for the food from that one who spoke to him.

Similarly, if the house of one for whom benefit is forbidden by a vow was to be built, his fence to be erected, or his field to be harvested, and laborers were required but he had no money to hire them, the one from whom benefit is forbidden goes to the laborers and says to them: Benefit from me is forbidden by vow to so-and-so and I do not know what I will do. And the laborers perform those tasks with him, and come and take payment for their labor from that person who approached them.

If the one who vowed to render benefit from him forbidden and the one for whom benefit is forbidden were traveling together along the road and the one for whom benefit is forbidden does not have anything to eat, the one who from whom benefit is forbidden gives food to one other person as a gift, and it is permitted for that person for whom benefit is forbidden to eat the food because it no longer belongs to the one from whom benefit is forbidden. If there is no other person with them, the one who vowed places the food on the nearest rock or on the nearest fence and says: These food items are hereby rendered ownerless and are available to anyone who wants them. Then that person for whom benefit is forbidden takes and eats the food. Rabbi Yosei prohibits doing so.

GEMARA: With regard to the dispute between the Rabbis and Rabbi Yosei whether one from whom benefit is forbidden to another can give the other person food by declaring the food ownerless, Rabbi Yoḥanan said: What is the reason for the opinion of Rabbi Yosei? He holds that the legal status of the process of rendering property ownerless is like that of the acquisition of a gift. Just as acquisition of a gift is not complete until the item comes from the possession of the one who gives the gift into the possession of the one who receives the gift, so too, the process of rendering property ownerless is not complete until the item comes into the possession of the one who acquires it. According to Rabbi Yosei, it is prohibited for the one for whom benefit is forbidden to take the food that was declared ownerless. Since it still belongs to the one from whom benefit is forbidden, by taking the food he derives forbidden benefit from him.

Rabbi Abba raises an objection from a baraita: And then that person takes and eats the food; and Rabbi Yosei prohibits doing so. Rabbi Yosei said: When is it prohibited to do so? When his vow predates his declaration that the food is ownerless. In that case, the vow took effect on all his possessions, including those that he later declared ownerless.

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

Nedarim 43a examines vow-based restrictions on lending, borrowing, and selling between parties, and debates the rabbinic reasoning behind these prohibitions.