Numbers 3:12-14

New Revised Standard Version Catholic Edition

¹² I hereby accept the Levites from among the Israelites as substitutes for all the firstborn that open the womb among the Israelites. The Levites shall be mine, ¹³ for all the firstborn are mine; when I killed all the firstborn in the land of Egypt, I consecrated for my own all the firstborn in Israel, both human and animal; they shall be mine. I am the Lord.

A Census of the Levites

¹⁴ Then the Lord spoke to Moses in the wilderness of Sinai, saying: