Leviticus 7:32-36

³²and ye shall give the right shoulder for a choice piece to the priest of your sacrifices of peace offering.

³³He that offers the blood of the peace offering, and the fat, of the sons of Aaron, his shall be the right shoulder for a portion.

³⁴For I have taken the wave breast and shoulder of separation from the children of Israel from the sacrifices of your peace offerings, and I have given them to Aaron the priest and his sons, a perpetual ordinance due from the children of Israel.

³⁵This is the anointing of Aaron, and the anointing of his sons, their portion of the burnt offerings of the Lord, in the day in which he brought them forward to minister as priests to the Lord;

³⁶as the Lord commanded to give to them in the day in which he anointed them of the sons of Israel, a perpetual statute through their generations.