Beitzah 39B

הרי אתה עלי חרם ⁠— הנודר אסור. הריני עליך ואתה עלי ⁠— שניהם אסורים זה בזה, ומותרין בשל עולי בבל, ואסורין בשל אותה העיר.

If he said to him: You are hereby prohibited to me by force of ḥerem, the one making the vow is himself prohibited to derive benefit from the addressee or from his property. If he said to him: I am hereby prohibited to you and you to me by force of ḥerem, they are both prohibited to benefit from one another. And they are permitted to benefit from anything belonging to those who come up from Babylonia, i.e., public property that is not owned by any person or group, but they are prohibited to benefit from property that is jointly owned by the inhabitants of that city, as both parties have a share in such items.

ואלו הן דברים של עולי בבל: הר הבית, הלשכות והעזרות, ובור של אמצע הדרך. ואלו הן של אותה העיר: הרחוב, ובית הכנסת, ובית המרחץ.

That Mishnah provides examples: And the following are items of those coming up from Babylonia, i.e., publicly owned items: The Temple Mount, the chambers, and the courtyards on the Temple Mount, and a cistern situated in the middle of the road. And these are items jointly owned by the inhabitants of that city: The street, and the synagogue, and the bathhouse.

ואי אמרת בירא דשותפי הוא, אמאי מותר? והתנן: השותפין שנדרו הנאה זה מזה ⁠— אסורים ליכנס לחצר לרחוץ בבור!

Rava, having cited the Mishnah in full, concludes his challenge to the opinion of Rav Naḥman: And if you say that a cistern of those who come up from Babylonia, a public cistern, is owned jointly by partners, i.e., by all Jews, why should it be permitted for the one who made the vow and the addressee to use it? But didn’t we learn in a Mishnah (Nedarim 45b): Two partners who took a vow not to derive benefit from one another are prohibited to enter a joint courtyard in which they both have a share to wash themselves in a cistern. According to you, the same should apply to a cistern in which the two of them have a share, such as the cisterns of those who come up from Babylonia.