Zevachim 26A

שחט ואחר כך חתך ⁠– פסולה.

But if he slaughtered the animal and after that severed its legs, the offering is disqualified because some of the blood collected is from the legs, which are outside the courtyard.

חתך ואחר כך שחט ⁠– כשרה?! בעל מום קא מקריב! אלא אימא: חתך ואחר כך קיבל ⁠– כשרה, קיבל ואחר כך חתך ⁠– פסולה.

The Talmud asks: If he severed its legs and after that slaughtered it, is the offering fit? But isn’t he sacrificing a blemished animal? Rather, say: If one slaughtered the animal while it stood wholly in the courtyard, and afterward its legs moved beyond the edge of the courtyard, and then he severed its legs and after that collected the blood, the offering is fit. But if he collected the blood and after that severed the animal’s legs, the offering is disqualified, since the blood from the legs is mixed with the other blood of the animal.

חתך ואחר כך קיבל ⁠– כשרה?! והא אמר רבי זירא: הצורם אזן בבכור, ואחר כך קיבל דמו ⁠– פסול; שנאמר: ״ולקח מדם הפר״⁠ – פר שהיה כבר!

The Talmud challenges: If he severed its legs and after that collected the blood, is the offering fit? But doesn’t R' Zeira say: If one slits the ear of a firstborn animal with the knife after slaughter, creating a blemish, and after that collected its blood from the neck, the offering is disqualified, as it is stated: “And the anointed priest should take from the blood of the bull” (Leviticus 4:5)? The verse indicates that the bull must be at the time of collection of the blood as it already was before slaughter, without a blemish.

אמר רב חסדא אמר אבימי: חותך באבר עד שמגיע לעצם.

Rav Ḥisda says that Avimi says: R' Ami is not referring to a case where one severs the entire leg. Rather, one cuts the flesh of the limb until he reaches the bone, leaving the bone intact. This is not considered a blemish, and the animal remains fit for sacrifice.