Sukkah 15A

מתני׳ תקרה שאין עליה מעזיבה, רבי יהודה אומר: בית שמאי אומרים: מפקפק, ונוטל אחת מבינתים. ובית הלל אומרים: מפקפק, או נוטל אחת מבינתים. רבי מאיר אומר: נוטל אחת מבינתים, ואינו מפקפק.

Mishnah: In the case of a roof made of boards that are 4 handbreadths wide upon which there is no coat of plaster, R' Yehuda says that Beit Shammai and Beit Hillel disagree with regard to the manner in which to render it fit. Beit Shammai say: One moves each board, and then it is considered as though he placed the board there for the sake of the mitzva of sukka, and one then removes one board from among the boards and replaces it with fit roofing. Beit Hillel say: One need not perform both actions; rather, one must either move the boards or remove one from among them. R' Meir says: One only removes one from among them and does not move the others.

גמ׳ בשלמא בית הלל, טעמייהו משום ״תעשה״ ולא מן העשוי. אי מפקפק, עביד ליה מעשה. אי נוטל אחת מבינתים, עבד בה מעשה. אלא בית שמאי, מאי טעמייהו? אי משום ״תעשה״ ולא מן העשוי ⁠— בחדא סגי! אי משום גזרת תקרה ⁠— בנוטל אחת מבינתים סגי!

Talmud: The Talmud asks: Granted, according to Beit Hillel, their reason for initially prohibiting this roof is due to the principle: Prepare it, and not from that which has already been prepared. If one moves the boards, he performs an action. Likewise, if he removes one of the boards from among them, he also performs an action. Therefore, in both cases, he prepared the roofing and the sukka is fit. However, with regard to the opinion of Beit Shammai, what is the rationale for their prohibition against using the original ceiling for a sukka? If the rationale is also due to the principle: Prepare it, and not from that which has already been prepared, one action should suffice. Or if the rationale is due to the decree of the roof, lest one come to reside beneath a regular plastered ceiling inside a house, removing one board from among them should suffice.