Numbers 4:27-28

27Aaron and his sons shall direct all the service of the sons of the Gershonites, all they have to carry and all they have to do. You shall assign to them as a duty all that they are to carry [on the march].

28This is the service of the families of the sons of Gershon in the Tent of Meeting (tabernacle); and their duties shall be under the direction of Ithamar the son of Aaron, the [high] priest.