Library Theodoret Compendium of Heretical Fables
Book 2
On Sabellius
Sabellius the Libyan, the Pentapolitan, began a heresy of this kind. He said that Father and Son and Holy Spirit are one hypostasis, and one person with three names, and that the same one is sometimes called Father, sometimes Son, sometimes Holy Spirit; and that in the Old he legislated as Father, in the New he became man as Son, and as Holy Spirit he came upon the apostles. Against him wrote Dionysius, bishop of the Alexandrians.
Greek: Theodoret of Cyrus, Haereticarum fabularum compendium / Αἱρετικῆς κακομυθίας ἐπιτομή (CPG 6223; PG 83, 336–556). English: study translation for BWAB Library—not a modern copyrighted translation. The full five books are hosted here.