26 You shall also speak to the Levites, and shall say to them, If you take the tithe from the children of Israel, which I have given you from them for an inheritance, then shall you separate from it a heave offering to the Lord, a tenth of the tenth.
Numbers 18:26 Cross References - CAB
Numbers 18:21
21 And behold, I have given to the sons of Levi every tithe in Israel for an inheritance for their services, the work in which they perform in the tabernacle of witness.
Nehemiah 10:38
38 And the priest, the son of Aaron, shall be with the Levites in the tithe of the Levite: and the Levites shall bring up their tithe to the house of our God, into the treasuries of the house of God.