Cyril's confession of the Word's nature
Cyril, bishop of Alexandria, is writing to Xystus, bishop of Rome, and begins with a first-person declaration of his own beliefs.
I have never been convicted of thinking anything contrary to what the truth approves, nor have I ever said that the divine nature of the Word is capable of suffering. And a little later: I know that the nature of God is incapable of suffering, unchangeable, and invariable, even in the nature of humanity, and that there is one Christ in both natures and from both natures.
Greek
Κυρίλλου ἐκ τῆς πρὸς Ἰούστον [ξορρ. Ξύστον] ἐπίσκοπον Ῥώμης ἐπιστολῆς. Ἐγὼ γὰρ οὔτε ἐλέγχομαι πεφρονηκὼς ἕτερόν τι πώποτε παρὰ τὸ δοκοῦν τῇ ἀληθείᾳ, οὔτε παθητὴν εἴρηκά ποτε τὴν θείαν τοῦ Λόγου φύσιν. Καὶ μετὰ βραχύ· Οἶδα δὲ καὶ ἀπαθῆ τὴν τοῦ Θεοῦ φύσιν καὶ ‹77.288› ἄτρεπτον καὶ ἀναλλοίωτον, κὰν τῇ τῆς ἀνθρωπότητος φύσει, καὶ ἕνα ἐν ἀμφοῖν καὶ ἐξ ἀμφοῖν τὸν Χριστόν.