Bava Metzia 70B

מתני׳ אין מקבלין צאן ברזל מישראל ⁠– מפני שהוא רבית. אבל מקבלין צאן ברזל מן הגוים,

Mishnah: One may not accept from a Jew sheep to raise or other items to care for as a guaranteed investment, in which the terms of the transaction dictate that the one accepting the item takes upon himself complete responsibility to repay its value in the event of depreciation or loss, but receives only part of the profit. This is because it is a loan, as the principal is fixed and always returned to the owner, and any additional sum the owner receives is interest. But one may accept a guaranteed investment from non-Jews, as there is no prohibition of interest in transactions with them.

ולוין מהן ומלוין אותן ברבית. וכן בגר תושב. מלוה ישראל מעותיו של נכרי ⁠– מדעת הנכרי, אבל לא מדעת ישראל.

And one may borrow money from them and one may lend money to them with interest. And similarly, with regard to a non-Jew who resides in Eretz Yisrael and observes the 7 Noahide mitzvot [ger toshav], one may borrow money from him with interest and lend money to him with interest, since he is not a Jew. Also, a Jew may serve as a middleman and lend a non-Jew’s money to another Jew with the knowledge of the non-Jew, but not with the knowledge of a Jew, i.e., the middleman himself, as the Talmud will explain.

גמ׳ למימרא דברשותא דמקבל קיימא? ורמינהו: המקבל צאן ברזל מן הגוים ⁠– ולדות פטורין מן הבכורה!

Talmud: With regard to the ruling that a guaranteed investment is considered a loan with interest, the Talmud asks: Is this to say that the guaranteed investment stands in the possession of the recipient, i.e., the recipient is viewed as its owner? And the Talmud raises a contradiction from a Mishnah (Bekhorot 16a): In the case of one who accepts from non-Jews an animal as a guaranteed investment, the offspring are exempt from the halakhot of a firstborn. This exemption apparently proves that the sheep still legally belong to the non-Jew owner.