Related for Beitzah 3:4
בְּכוֹר שֶׁנָּפַל לְבוֹר, רַבִּי יְהוּדָה אוֹמֵר, יֵרֵד מֻמְחֶה וְיִרְאֶה, אִם יֶשׁ בּוֹ מוּם, יַעֲלֶה וְיִשְׁחֹט. וְאִם לָאו, לֹא יִשְׁחֹט. רַבִּי שִׁמְעוֹן אוֹמֵר, כֹּל שֶׁאֵין מוּמוֹ נִכָּר מִבְּעוֹד יוֹם, אֵין זֶה מִן הַמּוּכָן:
A bechor (a first-born beast) which fell into a hole [A bechor with a blemish which he did not show to a sage before the festival to have it permitted — If it fell into a hole on yom tov and he feared that it might die there], let an expert go down [who can distinguish between a permanent blemish and a passing one] and examine [the blemish that he noticed yesterday to determine whether it is a permanent one]. If it had a (permanent) blemish, he may bring it up and slaughter it. [i.e., If the pre-yom tov blemish were not permanent, but it sustained a permanent blemish today, even if he transgressed and brought it up, he may not slaughter it. We do not say: His mind was set on it yesterday and since it now has a permanent blemish, let him slaughter it. For since yesterday's blemish was not permanent, it is muktzeh by reason of prohibition (of slaughtering an unblemished bechor).] R. Shimon says: Any animal whose blemish was not recognized (as a permanent one) before yom tov is not considered ready (for use on yom tov). [He forbids it not because of muktzeh, for muktzeh does not obtain according to R. Shimon. (He forbids it, rather,) because permitting it on yom tov is like amending it, and seems like the pronouncing of a ruling on yom tov, which was decreed against by reason of shvuth ("resting"). The intent (of the Mishnah, then,) is: His (the sage's) sanction is no sanction, and it is not "ready" to be considered kosher.]