Irenaeus

But that both the apostles and their disciples thus taught as the Church preaches, and thus teaching were perfected, wherefore also they were called away to that which is perfect-Stephen, teaching these truths, when he was yet on earth, saw the glory of God, and Jesus on His right hand, and exclaimed, "Behold, I see the heavens opened, and the Son of man standing on the right hand of God." These words he said, and was stoned; and thus did he fulfil the perfect doctrine, copying in every respect the Leader of martyrdom, and praying …

Against Heresies 3:12.13 ↗