Even if one should give away all his possessions in the world, and yet be in communion with heresy, he cannot be a friend of God, but rather is an enemy. St. Theodore the Studite
We forbid all the clergy who adhere to the Orthodox and Ecumenical Council in any way to submit to the bishops who have already apostatized or shall hereafter apostatize. Third Canon, Third Ecumenical Council
Whosoever transgresseth and abideth not in the doctrine of Christ hath not God. He that abideth in the doctrine of Christ, he hath both the Father and the Son. If there come any unto you and bring not this doctrine, receive him not into your house, neither bid him God speed: For he that biddeth him God speed is partaker of his evil deed.
II John 9-11
It is possible to find a middle word that between two views will signify both. But a middle view between two opposite views concerning the same thing is impossible…There is no room for compromise in matters of the Orthodox Faith. St. Mark of Ephesus
I adjure all the people in Cyprus who are true children of the Catholic Church to flee as fast as their feet can carry them from those priests who have fallen and submitted to the Latins [Roman Catholics]; neither assemble in church with them, nor receive any blessing from their hands. For it is better for you to pray to God in your homes alone than to gather together in churches with the Latin-minded. – Germanos II, Patriarch of Constantinople (620 A.D)
I am convinced that the further I depart from him [the Patriarch] and from those like him [the Latin-minded], the closer do I draw near to God and to all the faithful and the holy Fathers; and the more I am separated from them, by so much more am I united to the truth and the holy Fathers. St. Mark of Ephesus (1440 A.D.)