Numbers 18:26-29

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

²⁷And this your heave offering shall be reckoned unto you, as though it were the corn of the threshingfloor, 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 ye shall give thereof the LORD’s heave offering to Aaron the priest.

²⁹Out of all your gifts ye shall offer every heave offering of the LORD, of all the best thereof, even the hallowed part thereof out of it.