Numbers 1:51-53

⁵¹And when the Tent of meeting goes forward, the Levites are to take it down; and when it is to be put up, they are to do it: any strange person who comes near it is to be put to death.

⁵²The children of Israel are to put up their tents, every man in his tent-circle round his flag.

⁵³But the tents of the Levites are to be round the Tent of meeting, so that wrath may not come on the children of Israel: the Tent of meeting is to be in the care of the Levites.