Deuteronomy 18:3-5

3“1Now this shall be the priests’ portion from the people, from those who offer a sacrifice, either an ox or a sheep: they shall give the priest the shoulder, 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 fleece of your sheep. 53For the Lord your God has chosen him and his sons from all your tribes, to 4stand to serve in the name of the Lord always.