Numbers 1:47-50

47The Levites, however, were not counted by the tribe of their ancestors,

48for Adonai told Moses saying,

49“Definitely you are not to number the tribe of Levi, nor take the sum of them among Bnei-Yisrael.

50Instead, you are to appoint the Levites over the Tabernacle of the Testimony, over all its implements and all pertaining to it. They are to carry the Tabernacle and all its utensils, tend to it and camp around it.