Numbers 8:12

8:12 When the Levites lay their hands on the heads of the bulls, offer the one for a purification offering and the other for a whole burnt offering to the Lord, to make atonement for the Levites.

Numbers 11:11

11:11 And Moses said to the Lord, “Why have you afflicted your servant? Why have I not found favor in your sight, that you lay the burden of this entire people on me?