Numbers 1:47-50

47The ancestral tribe of the Levites, however, was not counted along with the others. 48The LORD had said to Moses: 49“You must not count the tribe of Levi or include them in the census of the other Israelites. 50Instead, appoint the Levites to be in charge of the tabernacle of the covenant law—over all its furnishings and everything belonging to it. They are to carry the tabernacle and all its furnishings; they are to take care of it and encamp around it.