Nedarim 67B

ולאו ממילא שמעת מינה?

The Talmud rejects this, stating: And do you not learn it by itself, from the words “And if she vowed in her husband’s house” (Numbers 30:11)? As the verse indicates that her husband can nullify only vows made after the couple is fully married, and not those made beforehand, the earlier verse is unnecessary.

איבעית אימא, דהויה קדושין משמע.

The Talmud suggests an alternative method of demonstrating that the first verse is referring to a betrothed woman: Or if you wish, say that the words “and if she be to a husband” (Numbers 30:7) must be referring to a betrothed woman, since the usage of the term “she be” indicates betrothal rather than marriage.

אימא אב לחודיה מיפר! אם כן ״ואסרה אסר בית אביה״, ״יניא אותה״ למה לי? השתא יש לומר במקום ארוס מיפר אב לחודיה, שלא במקום ארוס, מיבעיא?

The Talmud proposes: Say that a father can nullify the vows of his betrothed daughter on his own. The Talmud responds: If so, why do I need the verse to teach that in a case where she binds herself with a bond in her father’s house, her father can disallow her, i.e., nullify her vow (see Numbers 30:4–6). Now when it can be said that in the presence of a betrothed, i.e., when she is betrothed, the father nullifies his daughter’s vows on his own, is it necessary to state that he can do so where there is no betrothed? Therefore, the fact that the Torah specifically states that the father nullifies her vows by himself when she is not betrothed indicates that he does not have that power when she is betrothed.

אימא אב ליבעי ארוס, וארוס לחודיה מיפר. וכי תימא: אב דכתב רחמנא למה לי, מיבעי ליה דאי הקים ⁠— הקים!

The Talmud suggests: Say that the father requires the betrothed’s participation in order to nullify his daughter’s vows but that the betrothed can nullify them on his own. And if you would say: If the woman’s betrothed can nullify them on his own, why do I need the reference to the father that God writes with regard to the vows of a betrothed young woman, implying that the participation of the father is necessary to nullify her vows. One can explain that the need to mention the father is necessary in order to teach us that if the father ratified the vow, it is ratified, and her betrothed can no longer nullify it.