Numbers 18:19

All the heave-offerings of the holy things which the children of Israel offer unto the Lord have I given thee, and thy sons and thy daughters with thee, by a statute forever; it is a covenant of salt forever before the Lord unto thee and to thy seed with thee, an indissoluble covenant, an inviolable agreement. Cf Leviticus 2:13. In this manner the priesthood of Aaron and his family was once more firmly established in Israel, to serve the people in upholding the fellowship between them and Jehovah.