Nedarim, Chapter Ten, Mishnah 4. This mishnah deals with the window of time in which the father and the husband hold the authority to annul vows, and with the measure that Torah scholars adopted so as not to let that moment slip away.
The two limitations we learned in the previous mishnah:
The husband: Once he has married his wife through nisuin, he can no longer annul retroactively the vows she made before that.
The father: He can annul his daughter's vows only while she is a na'arah and betrothed. Once she has become married, or once she has become a bogeres, his authority to annul lapses.
The practice of Torah scholars:
In light of these limitations, Torah scholars would provide the remedy in advance: before the daughter left her father's domain to marry her husband, he would say to her: "Kol nedarim shenadart b'soch beisi harei hen mufar" - all the vows you made while in my house and under my authority are annulled. In this way everything is covered.
And likewise the husband, "ad shelo tikanes lirshuso" - before she entered his domain for nisuin, says to her: "Kol nedarim shenadart ad shelo tikansi lirshusi harei hen mufar". That is, all the vows she made while she was still a na'arah, before entering his domain, at a time when it is still in his power to annul her earlier vows - they are annulled. This statement is made before she has become his fully married wife.
And the reason for this: once she has entered his domain for nisuin, he can no longer annul the vows she made beforehand, and therefore he acts in advance and annuls them while she is still outside his domain.
In summary: In this mishnah we learned that because the father's authority to annul is limited to the period of na'arus and betrothal, and the husband's authority does not apply retroactively to vows that preceded the marriage, Torah scholars adopted the practice of annulling in advance: the father before his daughter left his house, and the husband before she entered his domain.