Zevachim 66A

אין צריך להבדיל. אמר ליה רב אחא בריה דרבא לרב אשי: אלא מעתה, גבי בור דכתיב ״ולא יכסנו״⁠ – הכי נמי דאין צריך לכסות?!

It means that the priest does not have to separate it, but not that it is prohibited to do so. Rav Aḥa, son of Rava, said to Rav Ashi: If that is so, then with regard to a pit in the public domain, where it is written: “And if a man should open a pit…and does not cover it” (Exodus 21:33), can one claim that this verse also means that he does not have to cover it?

הכי השתא?! התם, כיון דכתיב ״בעל הבור ישלם״⁠ – עלויה הוא דרמי לכסויי. אבל הכא, מכדי כתיב ״והקריבו״⁠ – חלק הכתוב בין חטאת העוף לעולת העוף;

The Talmud responds: How can these cases be compared? There, with regard to a pit, since it is written in the following verse: “The owner of the pit should pay” (Exodus 21:34), it is evident that it is incumbent upon him to cover the pit. But here, since it is written with regard to a bird burnt offering: “And the priest should bring it to the altar” (Leviticus 1:15), the term “it” indicates that the verse is referring only to a burnt offering, and the verse has thereby differentiated between a bird sin offering and a bird burnt offering.

״לא יבדיל״ למה לי? שמע מינה: אין צריך להבדיל.

Consequently, it is obvious that whereas the priest must completely separate the head of a bird burnt offering, this is not the halakha with regard to a sin offering. Why do I need the verse to state with regard to a bird sin offering: “But should not separate it” (Leviticus 5:8)? Conclude from this verse that it is not forbidden to separate the head of a bird sin offering from the body, but rather one does not have to separate it.