Polycarp: Epistle to the Philippians - c. 108 A.D.

"But Polycarp also was not only instructed by apostles, and conversed with many who had seen Christ, but was also, by apostles in Asia, appointed bishop of the Church in Smyrna, whom I also saw in my early youth, for he tarried [on earth] a very long time, and, when a very old man, gloriously and most nobly suffering martyrdom, departed this life, having always taught the things which he had learned from the apostles, and which the Church has handed down, and which alone are true. To these things all the Asiatic Churches testify....

There is also a very powerful Epistle of Polycarp written to the Philippians, from which those who choose to do so, and are anxious about their salvation, can learn the character of his faith, and the preaching of the truth. "

Irenaeus: Against Heresies (Book III, Chapter 3)