Numbers 18:26-30

²⁶“Moreover, you shall speak to the Levites and say to them, ‘When you take from the sons of Israel the tithe which I have given you from them for your inheritance, then you shall present an offering from it to the Lord, a tithe of the tithe. ²⁷Your offering shall be credited to you like the grain from the threshing floor or the full produce from the wine vat. ²⁸So you shall also present an offering to the Lord from all your tithes, which you receive from the sons of Israel; and from it you shall give the Lord’s offering to Aaron the priest. ²⁹Out of all your gifts you shall present every offering due to the Lord, from all the best of them, the sacred part from them.’ ³⁰And you shall say to them, ‘When you have offered from it the best of it, then the rest shall be credited to the Levites like the product of the threshing floor, and like the product of the wine vat.