Numbers 18:21, 26

As for the tribe of Levi, your relatives, I will compensate them for their service in the Tabernacle. Instead of an allotment of land, I will give them the tithes from the entire land of Israel.

“Give these instructions to the Levites: When you receive from the people of Israel the tithes I have assigned as your allotment, give a tenth of the tithes you receive—a tithe of the tithe—to the LORD as a sacred offering.