Numbers 18:26-29

²⁶“Moreover you shall speak to the Levites, and tell them, ‘When you take of the children of Israel the tithe which I have given you from them for your inheritance, then you shall offer up a wave offering of it for the LORD, a tithe of the tithe.

²⁷Your wave offering shall be credited to you, as though it were the grain of the threshing floor, and as the fullness of the wine press.

²⁸Thus 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.

²⁹Out of all your gifts, you shall offer every wave offering to the LORD, of all its best parts, even the holy part of it.’