St. Cyprian of Carthage, Letter to Cornelius of Rome 59 (55), 14 (252
AD)
With a false bishop appointed for themselves by heretics, they dare even
to set sail and carry letters from schismatics and blasphemers to the chair
of Peter and to the principal Church, in which sacerdotal unity has its
source; nor did they take thought that these are Romans, whose faith was
praised by the preaching Apostle, and among whom it is not possible for
perfidy to have entrance.
Pope St. Zosimus, Epistle to the Africans 11 (417 AD)
Although the tradition of the Fathers has assigned so great an authority to
the Apostolic see, that no one should dare to dispute about a judgment
given by it, and that See, by laws and regulations, has kept to this
you
know, dearest brethren, and as priests you are not ignorant, that we rule
over his place, and are in possession also of the authority of his name,
nevertheless, though so great be our authority that none may refuse our
sentence, we have not done anything, which we have not, of our will
referred by letter to your knowledge, conceding this to the Brotherhood.
St. Augustine of Hippo, Sermons 131, 10 (inter 391-430 AD)