Numbers 8:17

8:17 For all the firstborn males among the Israelites are mine, both humans and animals; when I destroyed all the firstborn in the land of Egypt I set them apart for myself.

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.”