Numbers 3:13-15

New Revised Standard Version Catholic Edition

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: ¹⁵ Enroll the Levites by ancestral houses and by clans. You shall enroll every male from a month old and upward.