Eruvin 68B

ניתיב מר בדוכתיה, וניבטיל להו לדידהו, וניהדרו אינהו וניבטלו ליה למר, דהא אמר רב: מבטלין, וחוזרין ומבטלין.

let the Master remain in his place, i.e., in the men’s chamber, and renounce his rights to his courtyard in favor of the residents of the baby’s courtyard, so that they may transfer the water from one courtyard to the other. And then, after the water has been moved, let them renounce their rights in favor of the Master, so that he may once again carry in his courtyard. As Rav said: If two people who live in the same courtyard forgot to establish an eiruv, one person may renounce his rights in favor of the other when he needs it, and the second person may then renounce his rights in favor of the first when he needs it.

אנא בהא כשמואל סבירא לי, דאמר: אין מבטלין וחוזרין ומבטלין.

Rava replied: In this regard, I hold in accordance with the opinion of Shmuel, who said: One person may not renounce his rights in favor of the other and then subsequently have the second person renounce his rights in favor of the first.

ולאו חד טעמא הוא? מאי טעמא אין מבטלין וחוזרין ומבטלין ⁠— לאו משום דכיון דבטליה לרשותיה, אסתלק ליה מהכא לגמרי, והוה ליה כבן חצר אחרת, ואין ביטול רשות מחצר לחצר. מר נמי, לא ניבטיל.

Ravina raised a difficulty: Isn’t the reason for both halakhot one and the same? What is the reason that one may not renounce his rights in favor of the other and then subsequently have the other renounce his rights in favor of the first? Is it not because it is assumed that since he renounced his rights to the courtyard, it is as if he has completely removed himself from here, and he is now considered like the resident of a different courtyard, and Shmuel holds that there is no renouncing of rights from one courtyard to another? If so, the Master should likewise not renounce his rights to his courtyard. If you accept Shmuel’s opinion with regard to subsequent renouncing, you should likewise accept his opinion with regard to renunciation of rights from one courtyard to another.