Numbers 18:27-28

²⁷And the gift which ye set apart shall be reckoned unto you, as though it were the corn of the threshing-floor, and as the fulness of the wine-press.

²⁸Thus ye also shall set apart a gift unto the LORD of all your tithes, which ye receive of the children of Israel; and thereof ye shall give the gift which is set apart unto the LORD to Aaron the priest.