Numbers 18:21-28

21“To the Levites I have given every tithe in Israel for an inheritance, in return for their service that they do, their service in the tent of meeting, 22so that the people of Israel do not come near the tent of meeting, lest they bear sin and die. 23But the Levites shall do the service of the tent of meeting, and they shall bear their iniquity. It shall be a perpetual statute throughout your generations, and among the people of Israel they shall have no inheritance. 24For the tithe of the people of Israel, which they present as a contribution to the LORD, I have given to the Levites for an inheritance. Therefore I have said of them that they shall have no inheritance among the people of Israel.” 25And the LORD spoke to Moses, saying, 26“Moreover, you shall speak and say to the Levites, ‘When you take from the people of Israel the tithe that I have given you from them for your inheritance, then you shall present a contribution from it to the LORD, a tithe of the tithe. 27And your contribution shall be counted to you as though it were the grain of the threshing floor, and as the fullness of the winepress. 28So you shall also present a contribution to the LORD from all your tithes, which you receive from the people of Israel. And from it you shall give the LORD’s contribution to Aaron the priest.