And to the Levites I hereby give all the tithes in Israel as their share in return for the services that they perform, the services of the Tent of Meeting. Henceforth, Israelites shall not trespass on the Tent of Meeting, and thus incur guilt and die: only Levites shall perform the services of the Tent of Meeting; others would incur guilt. It is the law for all time throughout the ages. But they shall have no territorial share among the Israelites; for it is the tithes set aside by the Israelites as a gift to the LORD that I give to the Levites as their share. Therefore I have said concerning them: They shall have no territorial share among the Israelites.
Numbers 18:21-24
If a Levite would go, from any of the settlements throughout Israel where he has been residing, to the place that the LORD has chosen, he may do so whenever he pleases. He may serve in the name of the LORD his God like all his fellow Levites who are there in attendance before the LORD. They shall receive equal shares of the dues,without regard to personal gifts or patrimonies.
Deuteronomy 18:6-8