Numbers 18:25-32

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.

29Out of all the gifts to you, you shall present every contribution due to the Lord; from each its best part is to be dedicated.'

30Therefore you shall say to them, 'When you have offered from it the best of it, then the rest shall be counted to the Levites as produce of the threshing floor, and as produce of the winepress.

31And you may eat it in any place, you and your households, for it is your reward in return for your service in the tent of meeting.

32And you shall bear no sin by reason of it, when you have contributed the best of it. But you shall not profane the holy things of the people of Israel, lest you die.'"