Shabbat 149B

וכדברי בית הלל אף משום רבית.

And according to Beit Hillel, they even violate the prohibition of interest. In Beit Hillel’s view, it is prohibited to loan or return objects without determining their monetary value, lest the object rise in value and the borrower end up returning an item that is more expensive than the one he borrowed.

אי הכי בניו ובני ביתו נמי! בניו ובני ביתו היינו טעמא ⁠— כדרב יהודה אמר רב. דאמר רב יהודה אמר רב: מותר להלוות בניו ובני ביתו ברבית כדי להטעימן טעם רבית.

The Talmud asks: If this is so, and one violates so many prohibitions when drawing lots, it should be prohibited to do so with one’s children and family members also. The Talmud answers: With regard to one’s children and family members, this is the reason that it is permitted: It is like the ruling that Rav Yehuda said that Rav said, for Rav Yehuda said that Rav said: It is permitted to loan to one’s children and family members with interest, in order to let them experience a taste of how difficult it is to repay a loan taken with interest. Also, in the case of family members, all the money, including the money used to repay the loan, belongs to the same person. Therefore, there is no real prohibition of interest.

אי הכי, מנה גדולה כנגד מנה קטנה נמי!

The Talmud asks: If this is so, and everything in this case actually belongs to the father, and he uses a lottery system in order to educate his family, it should be permitted to cast lots for a big portion against a small portion also.

אין הכי נמי, וחסורי מיחסרא והכי קתני: מפיס אדם עם בניו ועם בני ביתו על השלחן אפילו מנה גדולה כנגד מנה קטנה. מאי טעמא? כדרב יהודה אמר רב. עם בניו ועם בני ביתו ⁠— אין, עם אחרים ⁠— לא. מאי טעמא? כדרב יהודה אמר שמואל. מנה גדולה כנגד מנה קטנה ⁠— אף בחול לאחרים אסור. מאי טעמא? משום קוביא.

The Talmud answers: Yes, it is indeed so, and the Mishnah is incomplete and it teaches the following: A person may draw lots with his children and his family members at the table, and he may even do so with a large portion against a small portion. What is the reason for this? It is in accordance with the ruling that Rav Yehuda said that Rav said. Although with one’s children and family members, yes, this is permitted, with others it is not. What is the reason for this? It is in accordance with the ruling that Rav Yehuda said that Shmuel said: Raffling a large portion against a small portion is prohibited to do for other people, even on a weekday. What is the reason? Due to the prohibition against gambling with dice, which is prohibited by rabbinic law as a form of theft.