Numbers 1:48-54

The Levites’ exclusion from the census

48 The LORD spoke to Moses:
49 You must not enlist the tribe of Levi, nor should you take their census along with the Israelites.
50 Rather, assign the Levites to the covenant dwelling, to all its equipment, and to everything that belongs to it. They will carry the dwelling and all its equipment, perform its religious ceremonies, and camp around the dwelling.
51 When it's time to break camp, the Levites will take down the dwelling; and when it's time to make camp, the Levites will set up the dwelling. Any other person who approaches will be put to death.
52 The Israelites will camp each in their own place under the banner of their own military unit.
53 But the Levites will camp around the covenant dwelling so that God's anger will not strike the Israelite community. The Levites will guard the covenant dwelling.
54 The Israelites did everything exactly as the LORD commanded Moses.