Numbers 18:24-28

24For the tithe of the children of Israel, which they offer as an heave offering unto the LORD, I have given to the Levites for an inheritance: therefore I have said unto them, Among the children of Israel they shall have no inheritance.

25And the LORD spake unto Moses, saying,

26Moreover thou shalt speak unto the Levites, and say unto them, When ye take of the children of Israel the tithe which I have given you from them for your inheritance, then ye shall offer up an heave offering of it for the LORD, a tithe of the tithe.

27And your heave offering shall be reckoned unto you, as though it were the corn of the threshing-floor, and as the fulness of the winepress.

28Thus ye also shall offer an heave offering unto the LORD of all your tithes, which ye receive of the children of Israel; and thereof ye shall give the LORD’S heave offering to Aaron the priest.