Deuteronomy 18:3-5

3“These are the parts the priests may claim as their share from the cattle, sheep, and goats that the people bring as offerings: the shoulder, the cheeks, and the stomach.

4You must also give to the priests the first share of the grain, the new wine, the olive oil, and the wool at shearing time.

5For the Lord your God chose the tribe of Levi out of all your tribes to minister in the Lord’s name forever.