26'Moreover 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 set apart of it a gift for the LORD, even a tithe of the tithe.
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.
29Out of all that is given you ye shall set apart all of that which is due unto the LORD, of all the best thereof, even the hallowed part thereof out of it.
Numbers 18
Numbers 18:26-29