John Cassian, On the Incarnation of the Lord, Against Nestorius VI.21: The authority of Holy Scripture teaches that Christ existed from all eternity

And yet to return to what we said before, though all these things are so, as we have stated: how do we read that Jesus Christ (whom you assert to be a mere man) was ever existing even before His birth of a Virgin, and how is He proclaimed by prophets and apostles as God even before the worlds? As Paul says: “One Lord Jesus, through whom are all things.” And elsewhere he says: “For in Christ were created all things in heaven and on earth, both visible and invisible.” The Creed too, which is framed both by human and Divine authority, says: “I believe in God the Father, and in the Lord Jesus Christ, His Son.” And after other clauses: “Very God of Very God; by whom both the worlds were framed and all things were made.” And further: “Who for us came and was born of the Virgin Mary, and was crucified, and was buried.”