Numbers 8:13-15

New Revised Standard Version, Anglicised

¹³ Then you shall have the Levites stand before Aaron and his sons, and you shall present them as an elevation-offering to the Lord.

¹⁴ Thus you shall separate the Levites from among the other Israelites, and the Levites shall be mine. ¹⁵ Thereafter the Levites may go in to perform service at the tent of meeting, once you have cleansed them and presented them as an elevation-offering.