Since, however, he quotes with especial care, as a proof in his domain, a certain companion in misery (suntalai/pwron), and associate in hatred (summisou/menon), with himself, for the cure of leprosy, I shall not be sorry to meet him, and before anything else to point out to him the force of the law figuratively interpreted, which, in this example of a leper (who was not to be touched, but was rather to be removed from all intercourse with others), prohibited any communication with a person who was defiled with sins, with whom the apostle also forbids us even to eat food, forasmuch as the taint of sins would be communicated as if contagious: wherever a man should mix himself with the sinner.
Source: Against Marcion Book IV