Kiddushin 66A

״שורך נרבע״ והלה שותק ⁠– נאמן, ותנא תונא: ושנעבדה בו עבירה, ושהמית על פי עד אחד או על פי הבעלים ⁠– נאמן. האי ״על פי עד אחד״, היכי דמי? אי דקא מודו בעלים, היינו ״על פי הבעלים״, אלא לאו דשתיק?

Your ox was used by a man for an act of bestiality and is therefore unfit for an offering, and the other, the owner of the ox, is silent, the witness is deemed credible. And the tanna of the Mishnah also taught (Bekhorot 41a): And with regard to an animal that was used for a transgression or that killed, if this is attested to by one witness or by the owner, he is deemed credible. The Talmud clarifies this case: What are the circumstances of this case of the Mishnah, where the knowledge is established by one witness? If the owner admits to the claim, this is the same as: By the owner. Rather, is it not referring to a case where the owner remains silent?

וצריכא, דאי אשמעינן הך קמייתא, אי לאו דקים ליה בנפשיה דעבד ⁠– חולין בעזרה לא הוה מייתי.

The Talmud comments: And each of these statements of Abaye is necessary. As, had he taught us only that first case, where the witness said someone ate forbidden fat, one might have said that he is deemed credible for the following reason: Were it not for the fact that he himself was convinced that he had committed a transgression, he would not commit the transgression of bringing a non-sacred animal to the Temple courtyard on the basis of the testimony of one witness. Consequently, his silence is evidently an admission.

אבל ״נטמאו טהרותיך״⁠ – מימר אמרינן: האי דשתיק ⁠– דסבר, חזי ליה בימי טומאתו.

But if the witness said: Your ritually pure foods were rendered ritually impure, and the accused was silent, we would say: The reason that he is silent and refrains from denying the claim is that he thinks he is not suffering any significant loss, as the food is fit for him to eat on his days of ritual impurity, because he is not required to destroy ritually impure foods.