Cosmas Indicopleustes, Prooemium in Psalmos, from Book 5 of his Topographia Christiana (TLG 4061.002), PG 88, Coll. 248-249, though the conclusion (inc. διαγράφομεν οὖν αὐτὸν τὸν Δαβιδ καθεζόμενον) is taken from [John Chrysostom] Prooemia in Psalmos (TLG 2062.197) PG 55 Col. 534.