Nedarim 4:6-7

Nedarim 4:6

If one is prohibited by a vow from benefitting from his friend, he may not lend to him nor borrow from him, neither utensils nor money, nor may he sell to or buy from him. Let’s say that a person asked his friend to lend him his cow and the friend replied that it was unavailable, so the first person declared, “Konam my field if I ever plow with it!” If he normally plows his field himself, he may not do so using this cow but others may. If others normally plow his field, then neither he nor they may do so using this cow.

Nedarim 4:7

If one is prohibited by a vow from benefitting from his friend and he has no food, the friend can go to a shopkeeper and say, “(The first person) is prohibited by a vow from benefitting from me and I don’t know what to do.” The shopkeeper may then deliver food to the person who vowed and bill the friend. If the one who vowed needed work done on his home, property or field but he had no money to pay the workers, the friend can go to the workmen and say, “(The first person) is prohibited by a vow from benefitting from me and I don’t know what to do.” The workers may then do the job for the person who vowed and bill the friend.