Nedarim 17B

אין נדר בתוך נדר! קשיא.

in this case there is no vow within a vow. The Talmud concludes: This question is difficult, although it is not a conclusive refutation.

תנן: יש נדר בתוך נדר, ואין שבועה בתוך שבועה. היכי דמי? אילימא דאמר ״הריני נזיר היום, הריני נזיר למחר״, דכוותה גבי שבועה: ״שלא אוכל תאנים״, וחזר ואמר ״שבועה שלא אוכל ענבים״⁠ — אמאי לא חלה שבועה על שבועה?

The Talmud raises several problems with the opinion of Rav Huna. We learned in the Mishnah: There is a vow within a vow, but there is no oath within an oath. What are the circumstances? If we say that the case of a vow within a vow is where one said: I am hereby a nazirite today, I am a hereby a nazirite tomorrow, that in the corresponding situation with regard to an oath within an oath, which will not take effect, is where one said: I hereby take an oath that I will not eat figs, and he then said: I hereby take an oath that I will not eat grapes, i.e., he took two separate oaths; if so, why does an additional oath not take effect where an oath was already made? It ought to take effect, as the second oath is not connected to the first one.

אלא היכי דמי דלא חלה שבועה על שבועה, כגון דאמר ״שבועה שלא אוכל תאנים״, וחזר ואמר ״שבועה שלא אוכל תאנים״, דכוותה גבי נזירות היכי דמי ⁠— דאמר ״הריני נזיר היום, הריני נזיר היום״, וקתני יש נדר בתוך נדר. קשיא לרב הונא!

Rather, what are the circumstances in which a second oath does not take effect after an oath was already made? For example: where one said: I hereby take an oath that I will not eat figs, and he again said: I hereby take an oath that I will not eat figs. In the corresponding situation with regard to naziriteship, what are the circumstances? It must be a case where one said: I am hereby a nazirite today, I am a hereby a nazirite today; and the Mishnah teaches that in this case there is a vow within a vow. This poses a difficulty to the opinion of Rav Huna, who holds that in this case the second vow does not take effect.