Numbers 1:47-51

The families from the tribe of Levi were not listed with the others, because the LORD had told Moses: “Do not count the tribe of Levi or include them with the other Israelites. Instead put the Levites in charge of the Holy Tent of the Agreement and everything that is with it. They must carry the Holy Tent and everything in it, and they must take care of it and make their camp around it. Any time the Holy Tent is moved, the Levites must take it down, and any time it is set up, the Levites must do it. Anyone else who goes near the Holy Tent will be put to death.