Deuteronomy 18:3-5

3This shall be the priests’ share from the people who offer a sacrifice, whether a bull or a sheep: the priests are to be given the shoulder, the jowls, and the stomach. 4You are to give them the firstfruits of your grain, new wine, and oil, and the first wool sheared from your flock. 5For the LORD your God has chosen Levi and his sons out of all your tribes to stand and minister in His name for all time.