Numbers 18:28-32

So you shall also present an offering to the Lord from all your tithes, which you receive from the sons of Israel; and from it you shall give the Lord’s offering to Aaron the priest.

Out of all your gifts you shall present every offering due to the Lord, from all the best of them, the sacred part from them.’

And you shall say to them, ‘When you have offered from it the best of it, then the rest shall be credited to the Levites like the product of the threshing floor, and like the product of the wine vat.

You may eat it anywhere, you and your households, for it is your compensation in return for your service in the tent of meeting.

And you will bring on yourselves no sin by reason of it when you have offered the best of it. But you shall not profane the sacred gifts of the sons of Israel, so that you do not die.’ ”