Numbers 18:21-24

18:21 See, I have given the Levites all the tithes in Israel for an inheritance, for their service which they perform – the service of the tent of meeting. 18:22 No longer may the Israelites approach the tent of meeting, or else they will bear their sin and die. 18:23 But the Levites must perform the service of the tent of meeting, and they must bear their iniquity. It will be a perpetual ordinance throughout your generations that among the Israelites the Levites have no inheritance. 18:24 But I have given to the Levites for an inheritance the tithes of the Israelites that are offered to the Lord as a raised offering. That is why I said to them that among the Israelites they are to have no inheritance.”

Numbers 18:26-28

18:26 “You are to speak to the Levites, and you must tell them, ‘When you receive from the Israelites the tithe that I have given you from them as your inheritance, then you are to offer up from it as a raised offering to the Lord a tenth of the tithe. 18:27 And your raised offering will be credited to you as though it were grain from the threshing floor or as new wine from the winepress. 18:28 Thus you are to offer up a raised offering to the Lord of all your tithes which you receive from the Israelites; and you must give the Lord’s raised offering from it to Aaron the priest.