Numbers 4:27-28

27All the service of the sons of the Gershonites, that is, all their loads and all their work, shall be performed at the 1command of Aaron and his sons; and you shall assign to them as a duty all their loads. 28This is the service of the families of the sons of the Gershonites in the tent of meeting; and their duties shall be 2under the direction of Ithamar the son of Aaron the priest.