Numbers 8:14-16

New Revised Standard Version, Anglicised

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. ¹⁶ For they are unreservedly given to me from among the Israelites; I have taken them for myself, in place of all that open the womb, the firstborn of all the Israelites.