Numbers 8:13

10 and you shall present the Levites before Yahweh. The children of Israel shall lay their hands on the Levites:

11 and Aaron shall offer the Levites before Yahweh for a wave-offering, on the behalf of the children of Israel, that it may be theirs to do the service of Yahweh.

12 The Levites shall lay their hands on the heads of the bulls: and offer you the one for a sin-offering, and the other for a burnt offering, to Yahweh, to make atonement for the Levites.

13 You shall set the Levites before Aaron, and before his sons, and offer them for a wave-offering to Yahweh.

14 Thus shall you separate the Levites from among the children of Israel; and the Levites shall be mine.

15 After that shall the Levites go in to do the service of the tent of meeting: and you shall cleanse them, and offer them for a wave-offering.

16 For they are wholly given to me from among the children of Israel; instead of all who open the womb, even the firstborn of all the children of Israel, have I taken them to me.