Nedarim 90A

ושרקיה טינא, ואתייה לקמיה דרב חסדא. אמר רבא: מאן חכים למיעבד כי הא מילתא אי לאו דרב אחא בר רב הונא, דגברא רבה הוא. דקסבר דכי היכי דפליגי רבנן ורבי נתן בהפרה ⁠— הכי נמי פליגי בשאלה.

And Rav Aḥa bar Rav Huna then smeared him with clay to protect him from the elements, as it was now prohibited for him to benefit from the world by wearing clothes. And he then brought him before Rav Ḥisda, to dissolve his vow. Rava said: Who is wise enough to act in this manner, if not Rav Aḥa bar Rav Huna, who is a great man? As he holds that just as the Rabbis and R' Natan disagree with regard to nullification, whether it is possible to nullify a vow that has yet to take effect, so too, they disagree with regard to a request made to a halakhic authority to dissolve a vow, whether it is possible to request dissolution of such a vow. Rav Aḥa bar Rav Huna’s plan was to have the vow go into effect, so that the man could request that it be dissolved.

ורב פפי אמר: מחלוקת בהפרה, דרבי נתן סבר: אין הבעל מיפר אלא אם כן חל נדר, דכתיב: ״וחפרה הלבנה״. ורבנן סברי: בעל מיפר אף על פי שלא חל נדר, דכתיב: ״מפר מחשבות ערומים״.

And Rav Pappi said with regard to this issue: The dispute between R' Natan and the Rabbis is with regard to nullification only, as R' Natan holds that a husband can nullify a vow only once the vow has taken effect, as it is written: “And the moon should be confounded [ḥafera]” (Isaiah 24:23). He employs this phrase as an allusion, interpreting the word ḥafera as if it were hafara, nullification, and concludes from here that only a vow that already exists, like the moon, can be nullified. And the Rabbis hold that a husband can nullify a vow even though the vow has not yet taken effect, as it is written: “He nullifies the thoughts of the crafty” (Job 5:12), implying that nullification pertains even to thoughts, to prevent them from going into effect.