Firmilian of Caesarea, Letter to Cyprian (Ep. 74/75) 16

You can see the kind of error and the depth of blindness in anyone who claims that remission of sins can be granted in the synagogues of heretics, yet refuses to remain in the foundation of the one Church that Christ once established on the rock. It becomes clear from this that Christ spoke to Peter alone: "Whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven" (Matt. 16:19). And again in the Gospel, when Christ breathed on the Apostles only, he said: "Receive the Holy Spirit. If you forgive anyone's sins, they are forgiven; if you retain anyone's sins, they are retained" (John 20:22–23). Therefore the power to remit sins was given to the Apostles, to the Churches they established when sent by Christ, and to the bishops who succeeded them by vicarious ordination. But the enemies of the one Catholic Church—the Church in which we stand—and our adversaries, who claim to have succeeded the Apostles, are seizing illicit priesthoods for themselves against us and erecting profane altars. What are they but Korah, Dathan, and Abiram, guilty of the same sacrilegious crime? They will suffer the same punishments as those rebels, along with those who side with them, just as the participants and supporters of that ancient rebellion perished by the same death.