Numbers 18:18-19

18:18 And their meat will be yours, just as the breast and the right hip of the raised offering is yours. 18:19 All the raised offerings of the holy things that the Israelites offer to the Lord, I have given to you, and to your sons and daughters with you, as a perpetual ordinance. It is a covenant of salt ¹  forever before the Lord for you and for your descendants with you.”

[18:19]  ¹ sn Salt was used in all the offerings; its importance as a preservative made it a natural symbol for the covenant which was established by sacrifice. Even general agreements were attested by sacrifice, and the phrase “covenant of salt” speaks of such agreements as binding and irrevocable. Note the expression in Ezra 4:14, “we have been salted with the salt of the palace.” See further J. F. Ross, IDB 4:167.