Numbers 1:47-50 NIV

47 The families of the tribe of Levi,1 however, were not counted2 along with the others.

References for Numbers 1:47

48 The LORD had said to Moses:
49 "You must not count the tribe of Levi or include them in the census of the other Israelites.
50 Instead, appoint the Levites to be in charge of the tabernacle3 of the Testimony4--over all its furnishings5 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.

References for Numbers 1:50