Numbers 18:26-29

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 a heave-offering of it for Jehovah, a tithe of the tithe.

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

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

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