Pesachim 99A

מכאן אמרו חכמים: יפה שתיקה לחכמים, קל וחומר לטפשים. שנאמר: ״אויל מחריש חכם יחשב״.

From here the rabbis stated: Silence is fitting for the wise, and a fortiori the same is true for fools. In the case under discussion, had neither side appointed the other to slaughter the Paschal lamb on its behalf, both offerings would be valid and would be consumed. When each side appointed the other to slaughter the Paschal lamb on its behalf, only the first one slaughtered may be eaten while the second one must be burned. This is as it is stated: “Even a fool, when he holds his peace, is considered wise; and he that shuts his lips is esteemed as a man of understanding” (Proverbs 17:28).

שנים שנתערבו פסחיהם וכו׳. לימא מתניתין דלא כרבי יהודה. דתניא: ״ואם ימעט הבית מהיות משה״, מלמד שמתמעטין והולכין, ובלבד שיהא אחד מבני חבורה קיים, דברי רבי יהודה. רבי יוסי אומר: ובלבד שלא יניחו את הפסח כמות שהוא!

The Mishnah addressed the question of what two individuals whose Paschal lambs were intermingled should do. The Talmud suggests: Let us say that the Mishnah is not in accordance with the opinion of R' Yehuda, as it was taught in a baraita that the verse which states: “And if the household be too little for a lamb” (Exodus 12:4) teaches that the members of the group may keep decreasing, meaning it is permissible for them to withdraw from the offering, provided one of the original members of the group remains; this is the statement of R' Yehuda. R' Yosei says: It is permissible for them to withdraw provided they do not leave the Paschal lamb for any amount of time on its own, without anyone registered for it. In the Mishnah, the two original owners forego their shares in their own Paschal lambs, and the only remaining members of each group are people who were added from the marketplace, who were not original owners from the time the animal was separated as a Paschal lamb. This is apparently not in accordance with the opinion of R' Yehuda.