Shevuot 20A

מסרבין בו לאכול.

importuning [mesarevin] him to eat.

מתניתין ⁠– בשאין מסרבין בו לאכול; ברייתא ⁠– במסרבין בו לאכול, וקאמר ״לא אכילנא״ ו״לא אכילנא״, דכי קא משתבע הכי קאמר: ״שבועה שלא אוכל״.

The Talmud explains: The Mishnah here is referring to a case where others are not importuning him to eat; therefore, his oath should be understood literally, as obligating himself to eat. The external Mishnah, in tractate Nedarim, is referring to a case where others are importuning him to eat and he is saying: I will not eat, I will not eat. Under those circumstances, when he takes an oath, this is what he is saying: On my oath I will not eat.

רב אשי אמר: תני ״שבועה שאי אוכל לך״. אי הכי, מאי למימרא? מהו דתימא: לישניה (דאיתקילא) [איתקילא] ליה, קא משמע לן.

Rav Ashi, offering a different resolution of the contradiction, says: Teach, i.e., revise the Mishnah in tractate Nedarim to say in the middle oath: On my oath I will not [she’i] eat of yours, i.e., using a different formulation for: On my oath I will not eat of yours. The Talmud asks: If so, what is the purpose of stating what is effectively the same oath twice? The Talmud answers: Lest you say that there is a concern that the oath was a slip of his tongue and he meant to take an oath that he will eat and instead said: I will not eat, the Mishnah teaches us that one need not be concerned that this is what occurred.

תנו רבנן: ״מבטא״⁠ – שבועה. ״איסר״⁠ – שבועה. איסור איסר: אם אתה אומר ״איסר״⁠ – שבועה, חייב; ואם לאו, פטור. ״אם אתה אומר איסר שבועה״?! והא אמרת: איסר ⁠– שבועה הוא!

§ A baraita states: “The clear utterance of her lips, with which she has bound her soul” (Numbers 30:7), is referring to an oath, and: “A bond with which she has bound her soul” (Numbers 30:5), is also referring to an oath. With regard to the prohibition invoked by the word “bond,” if you say a bond is an oath, he is liable, but if not, he is exempt. The Talmud seeks to explicate this baraita: If you say a bond is an oath? But you already said that a bond is an oath.