Numbers 8:11

And Aaron shall separate the Levites for a gift before the Lord from the children of Israel: and they shall be prepared to perform the works of the Lord.

And Aaron shall offer the Levites before the Lord for an offering of the children of Israel, that they may execute the service of the Lord.

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.