Numbers 8:14-18

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. 8:17 For all the firstborn males among the Israelites are mine, both humans and animals; when I destroyed all the firstborn in the land of Egypt I set them apart for myself. 8:18 So I have taken the Levites instead of all the firstborn sons among the Israelites.