Numbers 18:8, 19

And the LORD spoke to Aaron: “Here, I Myself have also given you charge of My heave offerings, all the holy gifts of the children of Israel; I have given them as a portion to you and your sons, as an ordinance forever.

“All the heave offerings of the holy things, which the children of Israel offer to the LORD, I have given to you and your sons and daughters with you as an ordinance forever; it is a covenant of salt forever before the LORD with you and your descendants with you.”