Numbers 18:27-28

²⁷And this your heave-offering shall be reckoned to you, as though it were the corn of the threshing-floor, and as the fullness of the wine-press.

²⁸Thus ye also shall offer a heave-offering to the LORD of all your tithes which ye receive of the children of Israel; and ye shall give of them the LORD'S heave-offering to Aaron the priest.