Deuteronomy 18:3-5

18:3 This shall be the priests’ fair allotment from the people who offer sacrifices, whether bull or sheep – they must give to the priest the shoulder, the jowls, and the stomach. 18:4 You must give them the best of your grain, new wine, and olive oil, as well as the best of your wool when you shear your flocks. 18:5 For the Lord your God has chosen them and their sons from all your tribes to stand and serve in his name permanently.