Bava Metzia 70A

ונהגו בני כופרא אגרא בשעת משיכה, פגרא בשעת שבירה. אטו במנהגא תליא מילתא? משום דמתניתא תניא ⁠– מנהגא.

And the men of pitch [benei kufera], i.e., sailors, are accustomed to paying rent at the time of pulling and paying for damage at the time of breakage. The Talmud asks: Is that to say that this matter depends on custom? Is there no halakha with regard to this issue? The Talmud answers: Because the baraita taught this, it is an acceptable custom and therefore permitted.

אמר רב ענן אמר שמואל: מעות של יתומים מותר להלוותן ברבית. אמר ליה רב נחמן: משום דיתמי נינהו (ספינא) [ספינן] להו איסורא?! יתמי דאכלי דלאו דידהו ליזלו בתר שבקייהו! אמר ליה: אימא לי איזי גופא דעובדא היכי הוה?

§ Rav Anan says that Shmuel says: It is permitted to lend with interest money belonging to orphans. Since the orphans are minors and exempt from mitzvot, the prohibition against taking interest does not apply to them. Rav Naḥman said to him: Because they are orphans we may feed them prohibited items? In harsher language, he added: Orphans that consume that which is not theirs will follow their deceased parent to the graveyard. It cannot be that this was Shmuel’s intention. Therefore, Rav Naḥman said to Rav Anan: Say to me now, what was the actual incident? What exactly did you hear Shmuel say?

אמר ליה: ההוא דודא דבני מר עוקבא דהוה בי מר שמואל, תקיל ויהיב ליה, תקיל ושקיל ליה. שקיל אגרא ושקיל פחתא. אי אגרא ⁠– לא פחתא, ואי פחתא ⁠– לא אגרא.

Rav Anan said to him: There was a certain kettle that belonged to the children of Mar Ukva, who were minor orphans, and this kettle was in the house of Mar Shmuel, who would rent it out on behalf of the orphans. Mar Shmuel would weigh it and then give it out, and when the renter returned it Mar Shmuel would weigh it and take it back, and he would take a rental fee for use of the kettle and would also take payment for depreciation of the kettle due to the reduction in the weight of the metal. In general, the halakha is that if he takes a rental fee, he should not take payment for depreciation, and if he takes payment for depreciation, this means the kettle was a loan, and therefore he should not take a rental fee, as by taking both, it is interest. Nevertheless, Mar Shmuel did so with the kettle belonging to Mar Ukva’s children, which means he rendered it permitted for the orphans to take interest.