Numbers 18:21; Numbers 18:26

21 "To the sons of Levi, behold, I have given all the tithe in Israel for an inheritance, in return for their service which they perform, the service of the tent of meeting.

26 "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.