Deuteronomy 18:3-5

3This is the share due the priests from the people who sacrifice a bull or a sheep: the shoulder, the internal organs and the meat from the head. 4You are to give them the firstfruits of your grain, new wine and olive oil, and the first wool from the shearing of your sheep,

5for the LORD your God has chosen them and their descendants out of all your tribes to stand and minister in the LORD ’s name always.