Nedarim 78B

מועדי ה׳ צריכין קידוש בית דין, שבת בראשית אין צריכה קידוש בית דין.

The Festivals of YHWH require sanctification by the court, as the Festival dates are established by the court’s determination of Rosh Chodesh, whereas Shabbat, which commemorates Creation, does not require sanctification by the court. Shabbat is sanctified every week independent of any court decision.

מועדי ה׳ צריכין מומחה, ואין פרשת נדרים צריכין מומחה, אפילו בית דין הדיוטות.

As for ben Azzai’s statement, it should be understood as follows: The Festivals of YHWH require an expert, as the start of the month, which is dependent upon the appearance of Rosh Chodesh, which in turn determines the Festivals, can be established only by a court composed of experts. But the portion on vows does not require an expert, i.e., vows can be dissolved even by a court of laymen. This explanation of the baraita given to Rav Asi bar Natan also serves to explain Beit Shammai’s source for the halakha that 3 laymen can dissolve vows.

והא בפרשת נדרים ״ראשי המטות״ כתיב! אמר רב חסדא ואיתימא רבי יוחנן: ביחיד מומחה.

The Talmud raises a difficulty: But in the portion on vows the phrase “the heads of the tribes” (Numbers 30:2) is written. How, then, can it be said that vows can be dissolved by laymen? Rav Ḥisda said, and some say it was R' Yoḥanan: From “the heads of the tribes,” the rabbis derive that vows can be dissolved by a single expert by himself, but 3 laymen also have that ability.

אמר רבי חנינא: השותק על מנת למיקט, מפר אפילו מכאן ועד עשרה ימים. מתיב רבא: אימתי אמרו מת הבעל נתרוקנה רשות לאב ⁠— בזמן שלא שמע הבעל, או ששמע ושתק, או ששמע והפר ומת בו ביום. אבל שמע וקיים, או ששמע ושתק ומת ביום של אחריו ⁠— אין יכול להפר.

§ R' Ḥanina says: A husband who is silent and does not formally nullify his wife’s vow in order to annoy [lemeikat] her, but intends to nullify it later, can nullify it even from now until 10 days later. Rava raised an objection to this from a baraita: When did they say that if the husband of a betrothed young woman dies, the authority to nullify the woman’s vows reverts to the father? The authority reverts to the father when the husband did not hear of her vow, or when he heard and was silent, or when he heard and nullified it and died on the same day. But if he heard and ratified it, or if he heard and was silent and died on the following day, he, the father, cannot nullify the vow.