Bekhorot 26B

דעיקר לאו לכפרה אתי ⁠— משהי לה, או דלמא, כיון דעולה נמי מכפרא אעשה ⁠— לא משהי לה?

being brought for atonement is not its primary function, there is a concern that one might keep it? Or perhaps, since a burnt offering also effects atonement for neglecting to perform a positive mitzva, one does not keep the animal longer than necessary.

תא שמע: התולש צמר מבכור תם, אף על פי שנולד בו מום, שחטו ⁠— אסור. טעמא דתולש, הא נתלש ⁠— שרי, וכל שכן עולה דלא משהי לה!

The Talmud suggests: Come and hear a resolution from a baraita: With regard to one who plucks the wool from an unblemished firstborn, even though it later developed a blemish and the owner then slaughtered it, use of the wool is prohibited. The Talmud infers: The reason use of the wool is prohibited is because he plucks it. But if it was torn out not by human intervention it is permitted. And this is correct all the more so with regard to a burnt offering, where one does not keep the animal any longer than necessary.

הוא הדין אפילו נתלש נמי אסור, והאי דקתני ״תולש״ להודיעך כחו דעקביא, דבבעל מום אפילו בתולש נמי שרי.

The Talmud rejects this proof: Actually, the same is true even if the wool of an unblemished firstborn animal was torn out by some other means; it is also prohibited. And the reason that the baraita teaches the halakha using the term: One who plucks, is to convey to you the far-reaching nature of the opinion of Akavya ben Mahalalel, as he maintains that in the case of a blemished animal, discussed in the latter clause of the baraita, even if one plucks the wool it is permitted. Since the latter clause discusses a case where one plucked the wool himself, it is inferred that the former clause discusses the same situation.