Numbers 8:9-11

8:9 You are to bring the Levites before the tent of meeting and assemble the entire community of the Israelites. 8:10 Then you are to bring the Levites before the Lord, and the Israelites are to lay their hands on the Levites; 8:11 and Aaron is to offer the Levites before the Lord as a wave offering from the Israelites, that they may do the work of the Lord.