Gittin 33B

לא בטלה כולה; ואי אזלי הנך כתבי ויהבי ⁠– ליכתבו וליתבו;

is not entirely invalidated; and therefore, even though the husband nullified the agency of part of the group, if these other people whose agency was never nullified go and write the bill of divorce and give it to the wife, let them write and give the bill of divorce. There is nothing to be concerned about, as their agency was never nullified. Since the bill of divorce that they deliver is valid, there is no reason to institute an ordinance that a husband can nullify the agency only in the presence of the entire group.

רבן שמעון בן גמליאל סבר: עדות שבטלה מקצתה בטלה כולה; והנך לא ידעי, ואזלי וכתבי ויהבי; ושרו אשת איש לעלמא.

Rabban Shimon ben Gamliel disagrees and holds: Testimony that was partially invalidated is entirely invalidated. And if the agency of part of the group was nullified when those agents were not in the presence of the rest of the group, then those others do not know that their agency has been nullified as well. And they might then go and write a bill of divorce and give it, and they will cause the court to mistakenly permit a married woman to marry anyone.

ואיבעית אימא: דכולי עלמא עדות שבטלה מקצתה לא בטלה כולה; והכא, היינו טעמא דרבן שמעון בן גמליאל ⁠– קסבר: מלתא דמתעבדא באפי עשרה ⁠– צריכא בי עשרה למישלפה.

And if you wish, say instead that everyone agrees that testimony that was partially invalidated is not entirely invalidated; and here, this is the reason of Rabban Shimon ben Gamliel that the husband can nullify his instructions only in the presence of all of the agents: He holds that a matter that is performed in the presence of 10 people requires the presence of 10 people to revoke it. Since the husband instructed 10 people to write the bill of divorce, he cannot revoke his instructions in the presence of only a portion of them.