Numbers 18:26-29

²⁶And unto the Levites shalt thou speak, and say unto them, When ye take from the children of Israel the tithes which I have given you from them for your inheritance: then shall ye separate therefrom a heave-offering of the Lord, the tenth part of the tithe.

²⁷And your heave-offering shall be reckoned unto you, like the corn of the threshing-floor, and as the fulness of the wine-press.

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

²⁹From all your gifts shall ye set apart every heave-offering of the Lord, from every best part thereof, its hallowed portion therefrom.