Numbers 18:24-28

24For I have given to the Levites as their inheritance the tithe that the Israelites present to the LORD as a contribution. That is why I told them that they would not receive an inheritance among the Israelites.”

25And the LORD instructed Moses, 26“Speak to the Levites and tell them: ‘When you receive from the Israelites the tithe that I have given you as your inheritance, you must present part of it as an offering to the LORD—a tithe of the tithe. 27Your offering will be reckoned to you as grain from the threshing floor or juice from the winepress. 28So you are to present an offering to the LORD from all the tithes you receive from the Israelites, and from these you are to give the LORD’s offering to Aaron the priest.