daf bit: Bava Metzia 75

[cellio]

The torah forbids usury, or lending at interest. Rav Yehudah said in the name of Shmuel: scholars may borrow from each other on interest, because, fully knowing that usery is forbidden, they merely present gifts to each other. Rav Yehudah said in Rav's name that one may lend to his sons and household on interest in order to teach them the bitterness of usury, but the sages disagree because it also teaches the happiness of being a lender in that situation. (75a)

Comments

[cellio]

Under some interpretations the ban only applies when lending money to Jews.