Sanhedrin 30A

וכל לישני דבי דינא, ולא הוה כתב בה ״במותב תלתא הוינא וחד ליתוהי״.

and all of the formulations of an enactment of the court were written in it. But only two were signed on it, and the following statement was not written in it: We were convened in a session of 3 judges, and one of the judges is no longer here, as he died or left for another reason. There was therefore room for concern that perhaps there were only two witnesses, and they wrote the document of admission improperly.

סבר רבינא למימר: היינו דריש לקיש. אמר ליה רב נתן בר אמי: הכי אמרינן משמיה דרבא, כל כי האי גוונא חיישינן לבית דין טועין.

Ravina thought to say that this is a case in which the principle of Reish Lakish, that witnesses do not sign a document unless the action was performed appropriately, applies. Rav Natan bar Ami said to him: This is what we say in the name of Rava: In any cases like this, we are concerned for the possibility of an erroneous court that thinks that two constitute a court.

אמר רב נחמן בר יצחק: אי כתב בה ״בי דינא״, תו לא צריך.

Rav Naḥman bar Yitzḥak says: If it was written in the document: We, the members of the court, convened, it is unnecessary for the deed to further state that one of the judges is no longer there, as a standard court consists of 3 judges.

ודילמא בית דין חצוף הוא? דאמר שמואל: שנים שדנו, דיניהן דין, אלא שנקראו בית דין חצוף. דכתב ביה: ״בי דינא דרבנא אשי״.

The Talmud asks: But perhaps it was an impudent court, as Shmuel says: With regard to two judges who convened a tribunal and judged, their verdict is a binding verdict; but because they contravened the rabbinic ordinance mandating that a court must be composed of 3 judges, they are called an impudent court. The Talmud answers: It was a document in which it was written: We, the members of the court of Rabbana Ashi, convened. Rav Ashi’s court presumably conformed to rabbinic protocol.