Numbers 3:11-13

11Then the Lord spoke to Moses:

12“Look, I myself have taken the Levites from among the Israelites instead of every firstborn who opens the womb among the Israelites. So the Levites belong to me,

13because 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.”