Numbers 4:1-6

ADONAI spoke to Moses and to Aaron saying, “Take a census of the sons of Kohath from among the sons of Levi, by their families and by their ancestral households, everyone from 30 years of age to 50, all who come to serve doing the work in the Tent of Meeting. “This is the task of the sons of Kohath in the Tent of Meeting—the most holy things. Whenever the camp is about to move out, Aaron and his sons are to take down the shielding curtain and cover the Ark of the Testimony with it. Then they are to cover this with porpoise hide, then spread over it a cloth of solid blue. Then they are to put its poles in place.