Deuteronomy 18:3-5

3“1Now this shall be the priests’ due from the people, from those who offer a sacrifice, either an ox or a sheep, of which they shall give to the priest the shoulder and the two cheeks and the stomach. 4You shall give him the 2first fruits of your grain, your new wine, and your oil, and the first shearing of your sheep. 53For the Lord your God has chosen him and his sons from all your tribes, to 4stand 5and serve in the name of the Lord forever.