Eruvin 7A

ורבי יהושע היא דלא משגח בבת קול.

and the latter statement is in accordance with the opinion of R' Yehoshua, who does not pay attention to a bat kol that attempts to intervene in matters of halakha, for according to him, the dispute between Beit Shammai and Beit Hillel has not yet been decided.

ואיבעית אימא, הכי קאמר: כל היכא דמשכחת תרי תנאי ותרי אמוראי דפליגי אהדדי כעין מחלוקת בית שמאי ובית הלל ⁠— לא ליעבד כי קוליה דמר וכי קוליה דמר, ולא כחומריה דמר וכי חומריה דמר. אלא, או כי קוליה דמר וכחומריה עביד, או כקוליה דמר וכחומריה עביד.

The Talmud suggests yet another resolution: And if you wish, say instead that this is what the baraita is saying: Wherever you find two tanna’im or two amora’im who disagree with each other in the manner of the disputes between Beit Shammai and Beit Hillel, one should not act either in accordance with the leniency of the one Master and in accordance with the leniency of the other Master, nor should one act in accordance with the stringency of the one Master and in accordance with the stringency of the other Master. Rather, one should act either in accordance with both the leniencies and the stringencies of the one Master, or in accordance with both the leniencies and the stringencies of the other Master.

מכל מקום קשיא!

All of this is suggested to explain the wording of the baraita. In any case, it is difficult to explain the law with regard to the alleyway in Neharde’a, concerning which they simultaneously adopted the stringencies of both Rav and Shmuel.

אמר רב נחמן בר יצחק: כוליה כרב עבדוה. דאמר רב הונא אמר רב: הלכה ואין מורין כן.

Rav Naḥman bar Yitzḥak said: In fact, they acted entirely in accordance with the opinion of Rav, and the reason that they required doors and did not rely on the opening in the form of a doorway alone is due to that which Rav Huna said that Rav said: This is the halakha; however, a public ruling is not issued to that effect ab initio. Although Rav maintains that an opening in the form of a doorway is sufficient in an open alleyway, a public ruling is not issued to that effect; rather, the ruling is stringent, in accordance with Ḥananya’s position, and requires doors.