Ketubot 41B

הא מני רבי יוסי הגלילי היא, דאמר: תם משלם חצי כופר.

As it can be explained: According to whose opinion is this baraita taught? It is according to the opinion of R' Yosei HaGelili, who said: The owner of an innocuous ox pays half the ransom. According to his opinion, the only differences between innocuous and forewarned oxen are those specified in the Mishnah.

תא שמע: ״המית שורי את פלוני״, או ״שורו של פלוני״, הרי זה משלם על פי עצמו. מאי לאו, בתם! לא, במועד.

The Talmud suggests: Come and hear an additional proof from the Mishnah. One who said: My ox killed so-and-so, or: My ox killed an ox belonging to so-and-so, this owner pays based on his own admission. What, is this not referring to an innocuous ox, for which he pays half the damage, proving that it is a payment of money and not a fine? The Talmud rejects the proof: No, the tanna is referring to a forewarned animal.

אבל בתם מאי, אינו משלם על פי עצמו? אדתני סיפא: עבדו של פלוני אינו משלם על פי עצמו, ניפלוג וניתני בדידה: במה דברים אמורים ⁠— במועד, אבל תם ⁠— אינו משלם על פי עצמו! כולה במועד קמיירי.

The Talmud asks: However, in the case of an innocuous ox, what is the halakha? If it is that he does not pay based on his own admission, then, rather than teaching the latter clause of the Mishnah: One whose ox killed a slave belonging to so-and-so does not pay based on his own admission, let him distinguish and teach the distinction within the case itself: In what case is this statement said? It is with regard to a forewarned ox; however, the owner of an innocuous ox does not pay based on his own admission. The Talmud rejects this proof: The entire Mishnah is speaking of a forewarned ox, and does not address the halakha of an innocuous ox at all. Therefore, no proof can be cited with regard to the nature of half the payment.