Numbers 1:49

46 even all those who were numbered were six hundred three thousand five hundred fifty.

47 But the Levites after the tribe of their fathers were not numbered among them.

48 For Yahweh spoke to Moses, saying,

49 Only the tribe of Levi you shall not number, neither shall you take the sum of them among the children of Israel;

50 but appoint you the Levites over the tent of the testimony, and over all the furniture of it, and over all that belongs to it: they shall bear the tent, and all the furniture of it; and they shall minister to it, and shall encamp round about the tent.

51 When the tent sets forward, the Levites shall take it down; and when the tent is to be pitched, the Levites shall set it up: and the stranger who comes near shall be put to death.

52 The children of Israel shall pitch their tents, every man by his own camp, and every man by his own standard, according to their hosts.