Numbers 3:13

3:13 because all the firstborn are mine. When I destroyed all the firstborn in the land of Egypt, I set apart for myself all the firstborn in Israel, both man and beast. They belong to me. I am the Lord.”

Numbers 18:15

18:15 The firstborn of every womb which they present to the Lord, whether human or animal, will be yours. Nevertheless, the firstborn sons you must redeem, and the firstborn males of unclean animals you must redeem.