Yevamot 25B

גזלן דדבריהם ⁠— כשר לעדות אשה, גזלן דדברי תורה ⁠— פסול לעדות אשה. נימא רב מנשה דאמר כרבי יהודה!

Although one who is considered a robber according to the words of the rabbis is unfit for other forms of testimony, he is fit as a witness for testimony that a woman’s husband died. A robber according to Torah law is unfit as a witness even for testimony that a woman’s husband has died. Should we say that what Rav Menashe said is in accordance with the opinion of R' Yehuda? R' Yehuda said in the Mishnah that one who is considered absolutely wicked because he admitted that he is a murderer is unfit for testifying to the death of a husband, but one who was merely present among a gang of murderers is not.

אמר לך רב מנשה: אנא דאמרי אפילו לרבנן ⁠— וטעמא דרבנן הכא כדרבא, דאמר רבא: אדם קרוב אצל עצמו, ואין אדם משים עצמו רשע.

The Talmud rejects this: Rav Menashe could have said to you: I am speaking even according to the opinion of the Rabbis. Although the Rabbis did not allow one who was wicked by Torah law to testify for a woman, a witness who admitted: I killed him, is nevertheless believed. And the rationale of the Rabbis here is in accordance with the opinion of Rava, as Rava disputed Rav Yosef’s opinion and said: Even if one said that he was willingly sodomized by this man, he is not believed concerning his own actions, because a person is his own relative. Consequently, he may not testify about himself, just as the testimony of any relative is disqualified. And furthermore, a person does not make himself wicked. His testimony with regard to his own actions is inadmissible because he is his own relative, but his testimony is accepted both to put a sodomizer to death or to render it permitted for a woman to remarry by saying that he killed her husband.