Ketubot 98B

כאן שנה רבי, הכל לבעל המעות, כדתניא: הוסיפו לו אחת יתירה, הכל לשליח, דברי רבי יהודה. רבי יוסי אומר: חולקין.

Here R' Yehuda HaNasi taught, i.e., it can be learned from this Mishnah that it is R' Yehuda HaNasi’s opinion that everything belongs to the owner of the money. If one earned a profit through the actions of his agent, the profit belongs to him and not to the agent, as it is taught in a baraita where the rabbis debate this matter: In a case where one sent an agent to the marketplace to purchase merchandise at a certain price, if in addition to items that the agent purchased they added for him one extra item, the entire profit belongs to the agent; this is the statement of R' Yehuda. R' Yosei says: The owner of the money and the agent split the profit.

והתניא, רבי יוסי אומר: הכל לבעל המעות! אמר רמי בר חמא: לא קשיא. כאן בדבר שיש לו קצבה, כאן בדבר שאין לו קצבה.

The Talmud asks: But isn’t it taught in a baraita that R' Yosei says: Everything belongs to the owner of the money? Rami bar Ḥama said: This is not difficult. Here the baraita is referring to an item that has a fixed price. If the seller added something, it is clear that the additional item is a gift, but it is unclear if the gift is meant for the agent or for the owner of the money, so it is split between the two. Whereas there, the baraita is referring to an item that does not have a fixed price, and one can say that any additional items that were given were not intended for the agent, but were part of the overall deal and belong to the owner of the money.