On the Duty of All Orthodox Christians

St. Vincent of Lerins died ca. 445

To preach any doctrine therefore to Catholic Christians other than what they have received never was lawful, never is lawful, never will be lawful: and to anathematize those who preach anything other than what has once been received, always was a duty, always is a duty, always will be a duty. (The Commonitory 9.25)

…[I]t is the sure characteristic of Catholics to keep that which has been committed to their trust by the holy Fathers, to condemn profane novelties, and, in the Apostle’s words, once and again repeated, to anathematize every one who preaches any other doctrine than that which has been received. (Gal. 2:9) (ibid. 24.63)

Nicea II 7th Ecumenical Council 787

We gladly embrace the Divine Canons, viz.: those of the Holy Apostles, of the Six Ecumenical Synods, as also of the local synods and of our Holy Fathers, as inspired by one and the same Holy Spirit. Whom they anathematize we also anathematize; whom they depose, we depose; whom they cut off, we cut off; and whom they subject to penalties, we also so subject. (Ancient Epitome of Canon 1)

Encyclical of the Eastern Patriarchs 1848

…[N]either Patriarchs nor Councils could then have introduced novelties amongst us, because the protector of religion is the very body of the Church, even the people themselves, who desire their religious worship to be ever unchanged and of the same kind as that of their fathers. (Paragraph 17)