ואמר רב יוסף פלוני רבעו לאונסו הוא ואחר מצטרפין להרגו לרצונו רשע הוא והתורה אמרה אל תשת רשע עד רבא אמר אדם קרוב אצל עצמו ואין אדם משים עצמו רשע
And Rav Yosef also says, with regard to distinguishing between the different aspects of a single testimony: If a man testifies that so-and-so sodomized him against his will, he and another witness may combine as a valid pair of witnesses to kill the defendant for the sin of homosexual sodomy (see Leviticus 18:22). But if the one who was sodomized testified that the accused sodomized him with his consent, he is testifying that he himself is wicked, having been complicit in the forbidden act, and the Torah said: “Do not put your hand with a wicked person to be an unrighteous witness” (Exodus 23:1). Therefore, the testimony is rejected. Rava says: A person is his own relative and therefore may not testify about himself. Therefore, a person cannot render himself wicked by his own testimony. As a result, he is deemed credible with regard to the sodomizer, but not with regard to himself. He remains a valid witness to convict the sodomizer in combination with another.