Mishnah for Nedarim 10:8
הֲפָרַת נְדָרִים, כָּל הַיּוֹם. יֵשׁ בַּדָּבָר לְהָקֵל וּלְהַחֲמִיר. כֵּיצַד. נָדְרָה בְּלֵילֵי שַׁבָּת, יָפֵר בְּלֵילֵי שַׁבָּת וּבְיוֹם הַשַּׁבָּת עַד שֶׁתֶּחְשָׁךְ. נָדְרָה עִם חֲשֵׁכָה, מֵפֵר עַד שֶׁלֹּא תֶחְשַׁךְ. שֶׁאִם חָשְׁכָה וְלֹא הֵפֵר, אֵינוֹ יָכוֹל לְהָפֵר:
The annulment of vows [viz. (Numbers 30:9): "And if on the day that her husband hear, he constrain her"] obtains the entire day [until it gets dark, it being written: "on the day that he hear." As to its being written (Ibid. 15): "from day to day," this is to apprise us that we are not to say: in the daytime, yes; at night, no. "from day to day" indicates that sometimes he has time to annul "from time to time" (i.e., a twenty-four hour period), as when she vowed in the beginning of the night.] There is in this a leniency and a stringency. [That is, sometimes there is only little time for annulment, and sometimes, ample time.] How so? If she vowed on Sabbath night, he can annul on Sabbath night and on the day of the Sabbath until it gets dark. If she vowed before it got dark, he can annul (only) until it gets dark. For if it got dark and he had not annulled it, he can no longer do so. ["Sabbath night" apprises us that vows may be annulled (mefirin) on the Sabbath, even not for the sake of the Sabbath. But a sage may absolve one of vows (matir) on the Sabbath only for the sake of the Sabbath. And even though he had time in the daytime, he may absolve him for the sake of the Sabbath. ("For if it got dark and he had not annulled it, etc.":) For annulment of vows obtains "from time to time" only if she had vowed in the beginning of the night. And vis-à-vis annulment (hafarah) it avails only if he says: "Mufar lach" ("It is annulled for you") as per the language of the verse. For the husband's annulment is from this time forward, as in (Genesis 17:14): "He has annulled (hefer) My covenant." And when a sage says: "Mutar lach ("It is absolved for you"); there is here neither vow nor oath," he uproots the vow from its very beginning. And if the sage used the term "hafarah," or the husband, the term "hatarah," there is neither absolution nor annulment. And if he (the husband) said: "If you did not vow, I bevow you," his words stand, and he need not say: "It stands for you." Since, even if he remained silent that entire day the vow would stand, then, with minimal speaking (on his part) it also stands. And on the Sabbath he says: "Take and eat," "Take and drink," and he does not annul as he does on a weekday, and the vow is voided of itself. And if he cannot compel her, he voids it in his heart and he need not utter it with his lips. And it is only with bitul (voiding) such as: "Take and eat," where he forces her to transgress her vow, that thinking in his heart avails, even if he did not utter it with his lips. But with hafarah (annulment), where he does not compel her to transgress her vow, he must utter it with his lips, annulment in the heart not availing.]