Nedarim 21B

מי דמי? גבי צונן, צדיקים אומרים מעט ועושין הרבה —

Are these cases comparable? Concerning the case of cold water, the righteous say little and do much. Therefore, when the host says to the other: Enter my house and drink a drop of cold water, he intended to offer him an entire meal. So too, the one who vows is referring to an entire meal and not literally to a drop of water. Therefore, he may drink a bit of cold water in the host’s house.

הכא ספיקא הוא, דלמא פחות מסלע ויותר על שקל קאמר, וזירוזין הוי, או דלמא דוקא קאמר, ונידרא הוי. תבעי.

But here it is uncertain. Perhaps when the seller says he will only accept more than a sela, he really intends to accept less than a sela, and when the buyer says he will not pay more than a shekel, he really intends to pay more than a shekel; and this is also an exhortation vow. Or, perhaps he meant specifically what He said: and it is a vow, because he did not intend to compromise on the price. The Talmud concludes: The dilemma remains unresolved.

אמר רב יהודה אמר רב אסי: ארבעה נדרים הללו צריכין שאלה לחכם. כי אמריתא קמיה דשמואל, אמר: תנא תני ״ארבעה נדרים התירו חכמים״, ואת אמרת צריכין שאלה לחכם?!

§ Rav Yehuda said that Rav Asi said: These 4 vows that are taught in the Mishnah still require a request made to a halakhic authority to dissolve them. Rav Yehuda continues: When I said this halakha before Shmuel, he said: The tanna teaches that the rabbis dissolved 4 vows, and you say they require a request made to a halakhic authority?

רב יוסף מתני לה להא שמעתא בהאי לישנא: אמר רב יהודה אמר רב אסי: אין חכם רשאי להתיר אלא כעין ארבעה נדרים הללו. קסבר אין פותחין בחרטה.

Rav Yosef taught this halakha in this manner: Rav Yehuda said that Rav Asi said: A halakhic authority is able to dissolve only a vow that is similar to these 4 vows in that it was not intended to be a vow at all but was simply expressed in the language of a vow. In addition, he can dissolve a vow taken by mistake. The Talmud comments: It can be derived from here that he holds that a halakhic authority does not broach dissolution based on regret. A halakhic authority must search for a factor that, had the one making the vow been aware of it at the time of the vow, he would not have vowed. Simply expressing regret about the vow is an insufficient basis on which to dissolve it.