Numbers 8:14-16

8:14 And so you are to separate the Levites from among the Israelites, and the Levites will be mine.

8:15 “After this, the Levites will go in to do the work of the tent of meeting. So you must cleanse them and offer them like a wave offering. 8:16 For they are entirely given to me from among the Israelites. I have taken them for myself instead of all who open the womb, the firstborn sons of all the Israelites.