Ketubot 62A

אורחא דמילתא כמה? אמר רב: חדש כאן, וחדש בבית. שנאמר: ״לכל דבר המחלקות הבאה והיוצאת חדש בחדש לכל חדשי השנה״. ורבי יוחנן אמר: חדש כאן ושנים בביתו, שנאמר: ״חדש יהיו בלבנון שנים חדשים בביתו״.

The Talmud explains its query: Although a man can legally make any agreement with his wife to limit her conjugal rights, how much is an acceptable manner for this matter? Rav said: The husband may spend a month here, in the study hall, and then must spend a month at home. The allusion to this is as it is stated with regard to reserve units serving in King David’s army: “In any matter of the courses, which came in and went out month by month throughout all the months of the year” (I Chronicles 27:1). And R' Yoḥanan said: He may spend one month here, in the study hall, and then two months in his home, as it is stated with regard to workers who worked in the construction of the Temple: “A month they were in Lebanon, and two months at home” (I Kings 5:28).

ורב נמי, מאי טעמא לא אמר מההיא? שאני בנין בית המקדש, דאפשר על ידי אחרים: ורבי יוחנן מאי טעמא לא אמר מההיא? שאני התם, דאית ליה הרווחה.

The Talmud asks: And what is the reason that Rav did not also say a proof from that source that R' Yoḥanan quoted? The Talmud answers: The construction of the Temple is different, since it is possible for this work to be performed by others, as there were many people involved in it, but with regard to Torah study, which cannot be performed by others, he is given permission to spend a month here and a month there. The Talmud further questions: And what is the reason that R' Yoḥanan did not say a proof from that source that Rav quoted? The Talmud answers: There, with regard to King David, it is different, since he gains profit from working for the king; since there is profit involved, his wife might be willing to forgo his staying with her. However, in general a woman wants her husband to spend most of his time at home, so with regard to Torah study, where there is no monetary profit, she will not waive her right for as long.