The Levi Shall Give A Tenth Of Tithes To God, Numbers 18-19.

Then the Lord said to Aaron: “You and your sons and your father’s house with you shall bear the iniquity related to the sanctuary, and you and your sons with you shall bear the iniquity associated with your priesthood. Therefore you and your sons with you shall attend to your priesthood for everything at the altar and behind the veil; and you shall serve. I give your priesthood to you as a gift for service, but the outsider who comes near shall be put to death.” “Behold, I have given the children of Levi all the tithes in Israel as an inheritance in return for the work which they perform, the work of the tabernacle of meeting. Then the Lord spoke to Moses, saying, “Speak thus to the Levites, and say to them: ‘When you take from the children of Israel the tithes which I have given you from them as your inheritance, then you shall offer up a heave offering of it to the Lord, a tenth of the tithe.
Numbers 18:1,7,21,25-26 - hNKJV