Numbers 1:47-51

The Levites, however, were not numbered among them by their fathers’ tribe. For the LORD had said to Moses, “Only the tribe of Levi you shall not number, nor shall you take their census among the sons of Israel [since they are unavailable to go to war]. But appoint the Levites over the tabernacle (sanctuary) of the Testimony, and over all its furnishings and all things that belong to it. They shall carry the tabernacle [when traveling] and all its furnishings, and they shall take care of it and camp around it. When the tabernacle is to go forward, the Levites shall take it down; and when the tabernacle is to [be set up for] camp, the Levites shall set it up. But the layman (non-Levite) who approaches the tabernacle shall be put to death.