The Faith of Faustinus the Presbyter, Presented to the Emperor Theodosius

The faith drawn up at Nicaea against the Arian heresy was sufficient: but because certain persons, with a perverse disposition, under the guise of a profession of that faith, change the words into impious ones, casting odium upon us, as though we defended the heresy of Sabellius as it were; in a few words we also mark, against Sabellius, the confession of the first faith, and against those who under the name of the catholic faith defend impious words, saying that there are three substances; whereas the catholic faith has always confessed one substance of the Father and of the Son and of the Holy Spirit. We believe in the Father, who is not the Son, but has a Son begotten of Himself without beginning, not made; and we believe in the Son, who is not the Father, but has a Father, of whom He was begotten, not made; and we believe in the Holy Spirit, who is truly the Spirit of God.

Whence we also confess one substance of the divine Trinity; because such as the Father is according to substance, such also did He beget the Son: and the Holy Spirit, not being a creature, but the Spirit of God, is not alien from the substance of the Father and the Son; but is Himself of the same substance with the Father and the Son, just as of the same deity. For as to those who think us to be Apollinarists, let them know that we execrate the heresy of Apollinaris no less than the Arian. But we marvel that those can be approved as catholics who confess three substances of the Father and of the Son and of the Holy Spirit. But even if they say that they do not believe the Son of God, or the Holy Spirit, to be a creature, yet they hold a view contrary to the pious faith when they say that there are three substances: for it follows that those who confess three substances confess three gods. Which expression the Catholics have always execrated.