Numbers 18:9, 19

This shall be thine of the most holy things, reserved from the fire: every oblation of their's, every meat offering of their's, and every sin offering of their's, and every trespass offering of their's, which they shall render unto me, shall be most holy for thee and for thy sons.

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 for ever: it is a covenant of salt for ever before the LORD unto thee and to thy seed with thee.