"He who abandons the See of Peter on which the Church was founded, falsely believes himself to be a part of the Church." (St Cyprian)
"But what is the greatness of his error, and what the depth of his blindness, who says that remission of sins can be granted in the synagogues of heretics, and does not abide on the foundation of the one Church which was once based by Christ upon the rock, may be perceived from this, that Christ said to Peter alone, “Whatsoever thou shalt bind on earth shall be bound in heaven, and whatsoever thou shalt loose on earth shall be loosed in heaven.” And again, in the Gospel, when Christ breathed on the apostles alone, saying, “Receive ye the Holy Ghost: whose soever sins ye remit they are remitted unto them, and whose soever sins ye retain they are retained.” Therefore the power of remitting sins was given to the apostles, and to the churches which they, sent by Christ, established, and to the bishops who succeeded to them by vicarious ordination. But the enemies of the one Catholic Church in which we are, and the adversaries of us who have succeeded the apostles, asserting for themselves, in opposition to us, unlawful priesthoods, and setting up profane altars, what else are they than Korah, Dathan, and Abiram, profane with a like wickedness, and about to suffer the same punishments which they did, as well as those who agree with them, just as their partners and abettors perished with a like death to theirs?
And in this respect I am justly indignant at this so open and manifest folly....that he who so boasts of the place of his episcopate, and contends that he holds the succession from Peter, on whom the foundations of the Church were laid, should introduce many other rocks and establish new buildings of many churches; maintaining that there is baptism in them by his authority. For they who are baptized, doubtless, fill up the number of the Church. But he who approves their baptism maintains, of those baptized, that the Church is also with them. Nor does he understand that the truth of the Christian Rock is overshadowed, and in some measure abolished, by him when he thus betrays and deserts unity...Moreover, how great sin have you heaped up for yourself, when you cut yourself off from so many flocks! For it is yourself that you have cut off. Do not deceive yourself, since he is really the schismatic who has made himself an apostate from the communion of ecclesiastical unity. For while you think that all may be excommunicated by you, you have excommunicated yourself alone from all...For what is more lowly or meek than to have disagreed with so many bishops throughout the whole world, breaking peace with each one of them in various kinds of discord at one time with the eastern churches..."(St. Cyprian)http://www.ccel.org/ccel/schaff/anf05.iv.iv.lxxiv.html