Numbers 18:24-27
English Standard Version
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.