Numbers 1:47-51

But the Levites were not listed along with them by their ancestral tribe. For the LORD spoke to Moses, saying, “Only the tribe of Levi you shall not list, and you shall not take a census of them among the people of Israel. But appoint the Levites over the tabernacle of the testimony, and over all its furnishings, and over all that belongs to it. They are to carry the tabernacle and all its furnishings, and they shall take care of it and shall camp around the tabernacle. When the tabernacle is to set out, the Levites shall take it down, and when the tabernacle is to be pitched, the Levites shall set it up. And if any outsider comes near, he shall be put to death.