Megillah 2B

ומוקים לה לברייתא כרבי יוסי בר יהודה.

and he establishes the baraita in accordance with the opinion of R' Yosei bar Yehuda, rather than R' Yehuda.

ומי אמר רבי יהודה ״בזמן הזה, הואיל ומסתכלין בה ⁠— אין קורין אותה אלא בזמנה״? ורמינהי, אמר רבי יהודה: אימתי ⁠— מקום שנכנסין בשני ובחמישי. אבל מקום שאין נכנסין בשני ובחמישי ⁠— אין קורין אותה אלא בזמנה.

The Talmud explains the apparent contradiction: And did R' Yehuda actually say that nowadays, since people look to the reading of the Megilla and use it to calculate when Passover begins, one may read the Megilla only in its designated time? The Talmud raises a contradiction from a Mishnah (5a): R' Yehuda said: When is one permitted to read the Megilla from the 11th of Adar? In a place where the villagers generally enter town on Monday and Thursday. However, in a place where they do not generally enter town on Monday and Thursday, one may read the Megilla only in its designated time, the 14th of Adar.

מקום שנכנסין בשני ובחמישי מיהא קרינן, ואפילו בזמן הזה! ומוקים לה לברייתא כרבי יוסי בר יהודה.

The Mishnah indicates that, at least in a place where the villagers enter town on Monday and Thursday, one may read the Megilla from the 11th of Adar even nowadays. And due to this contradiction, Rav Ashi establishes the baraita in accordance with the opinion of R' Yosei bar Yehuda.

ומשום דקשיא ליה דרבי יהודה אדרבי יהודה מוקים לה לברייתא כרבי יוסי בר יהודה?!

The Talmud expresses surprise: Because Rav Ashi poses a difficulty due to the apparent contradiction between the opinion of R' Yehuda in the baraita and the opinion cited in a Mishnah in the name of R' Yehuda, he establishes the baraita in accordance with the opinion of R' Yosei bar Yehuda? How could he have emended the text just because he had a difficulty that he did not know how to resolve?

רב אשי שמיע ליה דאיכא דתני לה כרבי יהודה ואיכא דתני לה כרבי יוסי בר יהודה, ומדקשיא ליה דרבי יהודה אדרבי יהודה, אמר: מאן דתני לה כרבי יהודה ⁠— לאו דווקא, מאן דתני לה כרבי יוסי בר יהודה ⁠— דווקא.

The Talmud explains: Rav Ashi heard that there were those who taught the baraita in the name of R' Yehuda, and there were those who taught it in the name of R' Yosei bar Yehuda. And since he had a difficulty with the apparent contradiction between one ruling of R' Yehuda and another ruling of R' Yehuda, he said: The one who taught it in the name of R' Yehuda is not precise, whereas the one who taught it in the name of R' Yosei bar Yehuda is precise, and in this way he eliminated the contradiction.