Numbers 4:1-4

Then the LORD spoke to Moses and Aaron, saying, “Take a census of the sons of Kohath from among the sons of Levi, by their families (clans), by their fathers’ households, from thirty years old and upward, even to fifty years old, all who enter the service to do the work in the Tent of Meeting (tabernacle). This is the work and responsibility of the sons of Kohath in the Tent of Meeting (tabernacle): the most holy things.