Numbers 8:16

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.

Numbers 18:6

18:6 I myself have chosen your brothers the Levites from among the Israelites. They are given to you as a gift from the Lord, to perform the duties of the tent of meeting.