Deuteronomy 18:3-5

"And this shall be the priest's due from the people, from them that offer a sacrifice, whether it be ox or sheep; and they shall give unto the priest the shoulder, and the two cheeks, and the maw. The firstfruit also of thy corn, of thy wine, and of thine oil, and the first of the fleece of thy sheep, shalt thou give him. For the LORD thy God hath chosen him out of all thy tribes, to stand to minister in the name of the LORD, him and his sons for ever" - Deuteronomy 18:3-5 KJV