Yevamot 83A

ליתה למתניתין מקמי ברייתא, דתניא: רבי יוסי אומר: אנדרוגינוס ⁠— בריה בפני עצמה הוא, ולא הכריעו בו חכמים אם זכר אם נקבה.

The Mishnah here, which states that according to R' Yosei a priest who is a hermaphrodite enables his wife to eat teruma, is not to be relied upon in the presence of a baraita that teaches otherwise. As it is taught in a baraita that R' Yosei says: A hermaphrodite is a creature to himself, and the rabbis did not determine whether he is a male or a female. He is consequently prohibited from marrying a woman, and if he does so he does not enable her to eat teruma.

אדרבה ליתה לברייתא מקמי מתניתין! מדשבקיה רבי יוסי לבר זוגיה ⁠— שמע מינה הדר ביה.

The Talmud asks: On the contrary, say that the baraita is not to be relied upon in the presence of the Mishnah here, as baraitot are generally considered less authoritative than mishnayot. The Talmud answers: From the fact that R' Yosei left his colleague, R' Shimon, as the Mishnah’s ruling is attributed to both R' Yosei and R' Shimon whereas the teaching of the baraita is reported only in the name of R' Yosei, learn from this that R' Yosei retracted his original opinion that he had maintained together with R' Shimon and reached a different conclusion.

ושמואל אמר: ליתה לברייתא מקמי מתניתין. אדרבה, ליתא למתניתין מקמי ברייתא, דהא שמעינן ליה לשמואל דחייש ליחידאה! הני מילי, כי לא מתעקרא מתניתין, אבל כי מתעקרא מתניתין ⁠— לא חייש.

And Shmuel said the reverse: The baraita is not to be relied upon in the presence of the Mishnah here. The Talmud asks: On the contrary, say that the Mishnah here is not to be relied upon in the presence of the baraita, as we have heard that Shmuel takes into consideration even an individual dissenting opinion appearing in a baraita. The Talmud answers: This applies only when the Mishnah itself is not thereby uprooted, as the baraita merely adds to it. But when the Mishnah is uprooted by a contrary statement taught in a baraita, he does not take it into consideration.