Abbot St. Theodore of Studion says in 816 [Letter II:129 to Sakellarios Leo in PG 99:1420A]:
“Let him [Patriarch St. Nicephorus of Constantinople] assemble a synod of those with whom he has been at variance, if it is impossible that representatives of the other Patriarchs should be present, a thing which might certainly be if the Emperor should wish the Western Patriarch [the Roman Pope] to be present, to whom is given authority over an ecumenical synod; but let him make peace and union by sending his synodical letters to the prelate of the First See.”
Theodore Abu Qurrah:
“You should understand that the head of the Apostles was St. Peter, to whom Christ said, ‘You are the rock; and on this rock I shall build my church, and the gates of hell will not overcome it.’ After his resurrection, he also said to him three times, while on the shore of the sea of Tiberius, ‘Simon, do you love me? Feed my lambs, rams and ewes.’ In another passage, he said to him, ‘Simon, Satan will ask to sift you like wheat, and I prayed that you not lose your faith; but you, at that time, have compassion on your brethren and strengthen them.’ Do you not see that St. Peter is the foundation of the church, selected to shepherd it, that those who believe in his faith will never lose their faith, and that he was ordered to have compassion on his brethren and to strengthen them? As for Christ’s words, ‘I have prayed for you, that you not lose your faith; but you, have compassion on your brethren, at that time, and strengthen them’, we do not think that he meant St. Peter himself. Rather, he meant nothing more than the holders of the seat of St. Peter, that is, Rome”
During the Iconoclastic Crisis, Stephen the Faster challenged the assembled Bishops at Hiereia saying:
“How can you call a council ecumenical when the bishop of Rome has not given his consent, and the canons forbid ecclesiastical affairs to be decided without the pope of Rome?”