Numbers 18:22-26

And the sons of Israel shall not come near the tent of meeting again, or they will bring sin on themselves and die.

Only the Levites shall perform the service of the tent of meeting, and they shall bear their own guilt; it shall be a permanent statute throughout your generations, and among the sons of Israel they shall have no inheritance.

For the tithe of the sons of Israel, which they offer as an offering to the Lord, I have given to the Levites as an inheritance; therefore I have said concerning them, ‘They shall have no inheritance among the sons of Israel.’ ”

Then the Lord spoke to Moses, saying,

“Moreover, you shall speak to the Levites and say to them, ‘When you take from the sons of Israel the tithe which I have given you from them for your inheritance, then you shall present an offering from it to the Lord, a tithe of the tithe.