Exodus 29:28

And it shall be Aaron's and his sons' by a statute forever from the children of Israel; for it is an heave-offering; and it shall be an heave-offering from the children of Israel of the sacrifice of their peace-offerings, even their heave-offering unto the Lord. These parts were taken from the peace-offerings and the heave-offerings of the children of Israel, lifted off to be given to the priests. This signified in general that the priests were to be nourished from the sacrifices of Israel, even as the Lord has now ordained that they who preach the Gospel should live of the Gospel.