Deuteronomy 18:1-18:5
The levitical priests, the whole tribe of Levi, shall have no territorial portion with Israel. They shall live only off the Lord‘s offerings by fire as their portion, and shall have no portion among their brother tribes: the Lord is their portion, as He promised them.
This then shall be the priests' due from the people: Everyone who offers a sacrifice, whether an ox or a sheep, must give the shoulder, the cheeks, and the stomach to the priest. You shall also give him the first fruits of your new grain and wine and oil, and the first shearing of your sheep. For the Lord your God has chosen him and his descendants, out of all your tribes, to be in attendance for service in the name of the Lord for all time.