Chapter XXI. The authority of Holy Scripture teaches that Christ existed from all eternity.
Works of St John Cassian (Institutes, Conferences, On the Incarnation) · Saint John Cassian
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.”
Cassian 5.80.2