Eusebius on Mark Persuaded to Write after Multiple Performances

Eusebius HE 2.15.1

And so greatly did the splendor of piety illumine the minds of Peter’s hearers that they were not satisfied with hearing once only, and were not content with the unwritten teaching of the divine Gospel, but with all sorts of entreaties they besought Mark, a follower of Peter, and the one whose Gospel is extant, that he would leave them a written monument of the doctrine which had been orally communicated to them. Nor did they cease until they had prevailed with the man, and had thus become the occasion of the written Gospel which bears the name of Mark.

From http://www.ccel.org/ccel/schaff/npnf201.iii.vii.xvi.html