Numbers 1:47-51

But the Levites were not numbered among them by their fathers’ tribe; for the LORD had spoken to Moses, saying: “Only the tribe of Levi you shall not number, nor take a census of them among the children of Israel; but you shall appoint the Levites over the tabernacle of the Testimony, over all its furnishings, and over all things that belong to it; they shall carry the tabernacle and all its furnishings; they shall attend to it and camp around the tabernacle. And when the tabernacle is to go forward, the Levites shall take it down; and when the tabernacle is to be set up, the Levites shall set it up. The outsider who comes near shall be put to death.