Numbers 18:31

Thus you also shall offer a wave offering to the LORD of all your tithes, which you receive of the children of Israel; and of it you shall give the LORD’s wave offering to Aaron the priest.

Out of all your gifts, you shall offer every wave offering to the LORD, of all its best parts, even the holy part of it.’

“Therefore you shall tell them, ‘When you heave its best from it, then it shall be credited to the Levites as the increase of the threshing floor, and as the increase of the wine press.

You shall bear no sin by reason of it, when you have heaved from it its best. You shall not profane the holy things of the children of Israel, that you not die.’”