Numbers 3:9-11

New Revised Standard Version Catholic Edition

⁹ You shall give the Levites to Aaron and his descendants; they are unreservedly given to him from among the Israelites. ¹⁰ But you shall make a register of Aaron and his descendants; it is they who shall attend to the priesthood, and any outsider who comes near shall be put to death.

¹¹ Then the Lord spoke to Moses, saying: