Numbers 18:21-24

21And unto the children of Levi, behold, I have given all the tithe in Israel for an inheritance, in return for their service which they serve, even the service of the tent of meeting. 22And henceforth the children of Israel shall not come nigh the tent of meeting, lest they bear sin, and die. 23But the Levites shall do the service of the tent of meeting, and they shall bear their iniquity: it shall be a statute for ever throughout your generations; and among the children of Israel they shall have no inheritance. 24For the tithe of the children of Israel, which they offer as a heave-offering unto Jehovah, I have given to the Levites for an inheritance: therefore I have said unto them, Among the children of Israel they shall have no inheritance.