Irenaeus of Lyons, Against Heresies 3.4

Therefore, since these demonstrations exist, there is no need to seek the truth from others any longer, for it is easy to receive it from the Church. The Apostles, like men depositing a treasure in a rich repository, have fully entrusted to her all things that belong to the truth, so that everyone who wishes may draw from her the drink of life. For this is the entrance to life; all the others, however, are thieves and robbers. On this account we must avoid them, but we must love and cling to the things that belong to the Church with the greatest diligence, laying hold of the tradition of the truth.

For consider: if a dispute arose over some minor question, would it not be necessary to turn to the most ancient churches, those in which the Apostles themselves dwelt, and to learn from them what is certain and clear regarding the present issue? What is more, if the Apostles had not even left us the Scriptures, would it not have been necessary to follow the order of tradition which they handed down to those to whom they entrusted the churches?

To this order many nations of barbarians assent, those who believe in Christ. They have salvation written in their hearts by the Spirit, without paper or ink, and they diligently preserve the ancient tradition. They believe in one God, the Maker of heaven and earth and all things in them, through Christ Jesus, the Son of God. Because of his surpassing love for his creation, he endured the birth from the Virgin, himself uniting man to God. He suffered under Pontius Pilate, rose again, was received in glory, and will come in glory as the Savior of those who are saved and the Judge of those who are judged. He will send into eternal fire those who distort the truth, and those who despise his Father and his coming.

These men, who have believed without written documents, are barbarians as far as our language is concerned; but as far as judgment, custom, and conduct go, they are most wise through faith and pleasing to God, living in all justice, chastity, and wisdom. If anyone should announce to them the inventions of the heretics, speaking in their own tongue, they will immediately stop their ears and flee far away, refusing even to endure such blasphemous talk. Thus, through that ancient tradition of the elders, they do not admit even into the conception of their minds whatever portentous speech the heretics utter. For there was no assembly among them, nor any instituted doctrine.

For before Valentinus came, those who are from Valentinus did not exist; nor before Marcion did those from Marcion exist; nor were there at all the remaining malignant opinions which we enumerated above to become the authors and inventors of their perversity. Valentinus came to Rome under Hyginus; he flourished under Pius, and remained until Anicetus. Cerdo, who preceded Marcion, also lived under Hyginus, the eighth bishop. He came often into the church and made confession, but he ended in this way: sometimes he taught secretly, sometimes he made confession, sometimes he was rebuked by some for the evil things he taught, and he kept away from the assembly of the godly. Marcion, succeeding him, grew strong under Anicetus, who held the tenth place in the episcopate. The rest, who are called Gnostics, received their beginnings from Menander, the disciple of Simon, as we have shown. Each one of them, whose opinion he adopted, became the father and bishop of his own sect. All these men rose up in their apostasy much later, during the intervening times of the Church.