Gittin 3A

משום עיגונא אקילו בה רבנן.

due to the possibility of desertion, i.e., that she may become like a deserted wife, the rabbis were lenient with her by saying that the agent who brought the bill of divorce is deemed credible, despite the fact that he is a single witness. This is to prevent women from becoming uncertain of their marital status as a result of the lack of testimony needed to ratify the bill of divorce.

האי קולא הוא?! חומרא הוא! דאי מצרכת ליה תרי ⁠– לא אתי בעל מערער ופסיל ליה; חד ⁠– אתי בעל ומערער ופסיל ליה!

The Talmud asks: Is this ruling a leniency? It is a stringency, since if you require two witnesses to testify with regard to the bill of divorce, her husband cannot come to contest and invalidate it, as his testimony will not be accepted against that of the two witnesses. However, if only one agent brings the bill of divorce, the husband can come and contest and invalidate the document.

כיון דאמר מר: בפני כמה נותנו לה? רבי יוחנן ורבי חנינא; חד אמר: בפני שנים, וחד אמר: בפני שלשה; מעיקרא מידק דייק, ולא אתי לאורועי נפשיה.

The Talmud answers: Since the Master says: In the presence of how many people must the agent who brings the bill of divorce give it to the woman? R' Yoḥanan and R' Ḥanina disagreed with regard to this issue. One said that he must deliver it to her in the presence of at least two people, and one said that he must deliver it to her in the presence of at least 3 people, as 3 individuals are considered a court. Therefore, at the outset the agent is careful to clarify the matter fully, and he will not act to his own detriment by bringing an invalid bill of divorce.