Yevamot 81A

לימא תיהוי תיובתא דרב המנונא, דאמר: שומרת יבם שזינתה פסולה ליבמה! לא: הוא הדין אפילו לאחר נמי, ואיידי דתנא רישא בדידיה, תנא נמי סיפא בדידיה.

should we say that this is a conclusive refutation of the opinion of Rav Hamnuna, who said: A widow waiting for her yavam, who engaged in an act of licentious sex, is disqualified from entering into levirate marriage with her yavam, like an ordinary married woman who committed adultery? The Talmud rejects this argument: No, this presents no difficulty for Rav Hamnuna, as it is possible that the same is true even in a case where she had sex with a different man, that she too would be disqualified from marrying into the priesthood. But since the tanna taught the first clause with regard to the yavam himself, he also taught the latter clause with regard to the yavam himself, even though the same halakha applies if she cohabitated with another.

וכן איילונית שחלצו לה אחין כו׳. טעמא דבעלוה. הא לא בעלוה ⁠— לא. כמאן? דלא כרבי יהודה, דאי רבי יהודה, האמר: איילונית זונה היא.

It is taught in the Mishnah: And similarly, with regard to a sexually underdeveloped woman, if one of the brothers performed ḥalitza with her he has not disqualified her, but if he had sex with her he has disqualified her. The Talmud infers from this wording that the reason for her disqualification is that he had sex with her; but if he did not have sex with her she is not disqualified. According to whose opinion was this clause of the Mishnah taught? One must say that it was not taught in accordance with the opinion of R' Yehuda. As, if one would claim that this teaching is in accordance with the opinion of R' Yehuda, didn’t he say that a sexually underdeveloped woman is considered like a woman who has had sex with a man forbidden to her by the Torah [zona], and so she is in any case disqualified from marrying into the priesthood?