Study Nedarim folio 15B with parallel Hebrew-English text, traditional commentary, and modern study tools. Free access to Babylonian Talmud online.
And this is a conclusive refutation of the opinion of Rav Yehuda.
The Talmud answers: When the Mishnah teaches this, it does not mean that before she went she was permitted to derive benefit from him ab initio. Rather, it means that if she derived benefit from him after the fact, she is in violation of: He shall not profane his word.
We learn further on (57b) that if the husband said to his wife: Deriving benefit from me until the festival of Sukkot is konam for you if you go to your father’s house until Passover, then, if she went before Passover, she is prohibited from deriving benefit from him until the festival of Sukkot, a
The Talmud infers: Only if she went before Passover is it prohibited for her to derive benefit from him. However, if she did not go it is not prohibited for her to do so. She may derive benefit from him, and there is no concern that she will subsequently go to her father’s house, transgressing the p
Rava said: The same is true, that even if she did not go, she is prohibited from deriving benefit from him. The difference is that if she went it is not only prohibited for her to derive benefit from him, but if she does so she is flogged; whereas if she did not go, it is merely prohibited for her