Eruvin 63A

רב המנונא אורי בחרתא דארגז בשני דרב חסדא.

Rav Hamnuna issued halakhic rulings in the town of Ḥarta De’argez during the years of Rav Ḥisda’s life, even though Rav Ḥisda was his teacher.

רבינא סר סכינא בבבל. אמר ליה רב אשי: מאי טעמא עבד מר הכי?

The Talmud relates that Ravina once examined a slaughterer’s knife in Babylonia to check if it was fit for slaughtering, during the lifetime of his teacher, Rav Ashi, who also lived in Babylonia. Rav Ashi said to him: What is the reason that the Master acted in this manner? Isn’t it prohibited for a disciple to issue rulings while his teacher is still alive?

אמר ליה: והא רב המנונא אורי בחרתא דארגז בשני דרב חסדא! אמר ליה: ״לאו אורי״ אתמר.

Ravina said to him: Didn’t Rav Hamnuna issue halakhic rulings in Ḥarta De’argez during the years of Rav Ḥisda’s life, as they were not in the same town, even though they were both located in Babylonia? Since I do not live in the same town as you, it stands to reason that I would be permitted to issue rulings as well. Rav Ashi said to Ravina: It was actually stated that Rav Hamnuna did not issue halakhic rulings during Rav Ḥisda’s lifetime, and that is the correct tradition.

אמר ליה: אתמר ״אורי״, ואתמר ״לא אורי״, בשני דרב הונא רביה הוא דלא אורי, ואורי בשני דרב חסדא, דתלמיד חבר דיליה הוה. ואנא נמי תלמיד חבר דמר אנא.

Ravina said to Rav Ashi: In fact, it was stated that Rav Hamnuna issued rulings, and it was also stated that he did not issue rulings, and both traditions are correct. During the years of the life of Rav Huna, Rav Hamnuna’s principal teacher, Rav Hamnuna did not issue rulings at all, but he did issue rulings during the years of Rav Ḥisda’s life, for Rav Hamnuna was Rav Ḥisda’s disciple-colleague. And since I, too, am the Master’s disciple and colleague, I should also be permitted to examine a slaughterer’s knife when I am not in the same town.