Números 4:27

27 All their service, whether carrying or doing other work, is to be done under the direction of Aaron and his sons. You shall assign to them as their responsibility all they are to carry.

27 At the commandment of Aaron and his sons shall be all the service of the sons of the Gershonites, in all their burden, and in all their service; and ye shall appoint unto them in charge all their burden.