Numbers 18:26-29

²⁶Say to the Levites, When you take from the children of Israel the tenth which I have given to you from them as your heritage, a tenth part of that tenth is to be offered as an offering lifted up before the Lord.

²⁷And this lifted offering is to be put to your credit as if it was grain from the grain-floor and wine from the vines.

²⁸So you are to make an offering lifted up to the Lord from all the tenths which you get from the children of Israel, giving out of it the Lord's lifted offering to Aaron the priest.

²⁹From everything given to you, let the best of it, the holy part of it, be offered as a lifted offering to the Lord.