Numbers 18:21-26 King James Version (KJV)
21 And, behold, I have given the children of Levi all the tenth in Israel for an inheritance, for their service which they serve, even the service of the tabernacle of the congregation.
22 Neither must the children of Israel henceforth come nigh the tabernacle of the congregation, lest they bear sin, and die.
23 But the Levites shall do the service of the tabernacle of the congregation, and they shall bear their iniquity: it shall be a statute for ever throughout your generations, that among the children of Israel they have no inheritance.
24 But the tithes of the children of Israel, which they offer as an heave offering unto the Lord, I have given to the Levites to inherit: therefore I have said unto them, Among the children of Israel they shall have no inheritance.
25 And the Lord spake unto Moses, saying,
26 Thus speak unto the Levites, and say unto them, When ye take of the children of Israel the tithes which I have given you from them for your inheritance, then ye shall offer up an heave offering of it for the Lord, even a tenth part of the tithe.