Números 18:26

26 "Speak to the Levites and say to them: 'When you receive from the Israelites the tithe I give you as your inheritance, you must present a tenth of that tithe as the Lord's offering.

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