Eruvin 23A

גמ׳ אמר רב יוסף אמר רב יהודה אמר שמואל: הלכה כרבי יהודה בן בבא. ואמר רב יוסף אמר רב יהודה אמר שמואל: לא הותרו פסי ביראות אלא לבאר מים חיים בלבד.

Talmud: Rav Yosef said that Rav Yehuda said that Shmuel said: The halakha is in accordance with the opinion of R' Yehuda ben Bava. And Rav Yosef also said that Rav Yehuda said that Shmuel said: Upright boards surrounding a well were permitted only in the case of a well containing potable, running spring water.

וצריכא: דאי אשמעינן הלכה כרבי יהודה בן בבא, הוה אמינא: דרבים ⁠— ואפילו מכונסין,

The Talmud comments: And it was necessary to cite both of these statements, even though their content appears to be the same. As had he taught us only that the halakha is in accordance with the opinion of R' Yehuda ben Bava that upright boards may only be set arranged for a well, I would have said that with regard to water belonging to the public, upright boards are permitted not only in the case of spring water, but even in the case of water collected in a cistern.

והאי דקתני באר הרבים ⁠— לאפוקי מדרבי עקיבא. קא משמע לן דלא הותרו פסי ביראות אלא לבאר מים חיים.

And that which was taught: One may only arrange boards for a public well, that was to exclude the opinion of R' Akiva that upright boards may be arranged even for a private well, but not to allow us to infer that boards may not be arranged for a public cistern filled with collected water. Therefore, Shmuel teaches us that boards surrounding a well were permitted only in the case of a well of spring water.

ואי אשמעינן באר מים חיים, הוה אמינא: לא שנא דרבים ולא שנא דיחיד, קא משמע לן: הלכה כרבי יהודה בן בבא.

And in the opposite direction, had he taught us that upright boards may only be arranged for a well containing potable, running spring water, I would have said that there is no difference whether it is a public well and there is no difference whether it is a private well. Shmuel therefore teaches us that the halakha is in accordance with the opinion of R' Yehuda ben Bava, who says that upright boards may be arranged only for a public well, but not for one that belongs to an individual.