Nedarim 8B

כך אי אפשר לחלום בלא דברים בטלים.

so too, it is impossible to dream without idle matter. It is possible that the excommunication was real and the dissolution was not real, and he must have the ostracism dissolved by 10 people.

רבינא הוה לה נדרא לדביתהו. אתא לקמיה דרב אשי, אמר ליה: בעל מהו שיעשה שליח לחרטת אשתו? אמר ליה: אי מכנפין ⁠— אין, אי לא ⁠— לא.

The Talmud relates that Ravina’s wife had taken a vow that he had not immediately nullified as a husband is entitled to do, and she wished to have it dissolved. Ravina came before Rav Ashi and said to him: What is the halakha with regard to whether a husband can become an agent to express his wife’s regret to a court so that they can dissolve her vow? Rav Ashi said to him: If 3 people who can dissolve the vow were already assembled, yes; if they are not already assembled, no, a husband cannot serve as an agent to express his wife’s regret to the court.

שמע מינה תלת. שמע מינה: בעל נעשה שליח לחרטת אשתו. ושמע מינה: לא שרי למישרי נדרא באתרא דרביה. ושמע מינה: כי מכנפין שפיר דמי.

The Talmud comments: Learn from this incident 3 halakhot: Learn from this that a husband can become an agent to express his wife’s regret. And learn from this that a Sage is not permitted to dissolve a vow in the location of his teacher, which is why Ravina, a distinguished Sage, did not dissolve the vow without consulting Rav Ashi. And learn from this that when 3 people were already assembled, it seems well for a husband to serve as an agent to express his wife’s regret, but if the 3 people were not yet assembled he cannot serve as her agent.

ושמתא ⁠— אפילו באתרא דרביה, ויחיד מומחה שרי שמתא.

The Talmud adds: And one may dissolve excommunication even in the location of his teacher. And an individual Sage who is an expert can dissolve excommunication even without two other judges.