Numbers 1:53

1:53 But the Levites must camp around the tabernacle of the testimony, so that the Lord’s anger will not fall on the Israelite community. The Levites are responsible for the care of the tabernacle of the testimony.”

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.