Numbers 18:28-30

New Revised Standard Version, Anglicised Catholic Edition

²⁸ Thus you also shall set apart an offering to the Lord from all the tithes that you receive from the Israelites; and from them you shall give the Lord’s offering to the priest Aaron. ²⁹ Out of all the gifts to you, you shall set apart every offering due to the Lord; the best of all of them is the part to be consecrated. ³⁰ Say also to them: When you have set apart the best of it, then the rest shall be reckoned to the Levites as produce of the threshing-floor, and as produce of the wine press.