Numbers 1:48

45 So all those who were numbered of the children of Israel, by their families, all those of twenty years old and over who were able to go to war,

46 Were six hundred and three thousand, five hundred and fifty.

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

49 Only the tribe of Levi is not to be numbered among the children of Israel,

50 But to them you are to give the care of the Tent of meeting with its vessels and everything in it: they are to take up the Tent, and be responsible for everything to do with it, and put up their tents round it.

51 And 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.