Irenaeus and Novatian on John 17:5

"In the beginning, therefore, did God form Adam, not as if He stood in need of man, but that He might have [some one] upon whom to confer His benefits. For not alone antecedently to Adam, but also before all creation, the Word glorified His Father, remaining in Him; and was Himself glorified by the Father, as He did Himself declare, 'Father, glorify Thou Me with the glory which I had with Thee before the world was'" (Irenaeus, Adversus Haereses 4.14.1).

"If, before the world was, He had glory with God, and maintained His glory with the Father, He existed before the world, for He would not have had the glory unless He Himself had existed before, so as to be able to keep the glory. For no one could possess anything, unless he himself should first be in existence to keep anything. But now Christ has the glory before the foundation of the world; therefore He Himself was before the foundation of the world. For unless He were before the foundation of the world, He could not have glory before the foundation of the world, since He Himself was not in existence. But indeed man could not have glory before the foundation of the world, seeing that he was after the world; but Christ had—therefore He was before the world. Therefore He was not man only, seeing that He was before the world. He is therefore God, because He was before the world, and held His glory before the world. Neither let this be explained by predestination, since this is not so expressed, or let them add this who think so, but woe is denounced to them who add to, even as to those who take away from, that which is written. Therefore that may not be said, which may not be added. And thus, predestination being set aside, seeing it is not so laid down, Christ was in substance before the foundation of the world" (Novatian, De Trinitate 16).