Patristics on Modalistic Monarchianism

 “While keeping to this demurrer always, there must, nevertheless, be place for reviewing for the sake of the instruction and protection of various persons. . . . This is especially so in the case of the present heresy [Sabellianism], which considers itself to have the pure truth when it supposes that one cannot believe in the one only God in any way other than by saying that Father, Son, and Spirit are the selfsame person. As if one were not all . . . through the unity of substance” (Against Praxeas 2:3–4 [A.D. 216]). - Tertullian

“[W]ho does not acknowledge that the person of the Son is second after the Father, when he reads that it was said by the Father, consequently to the Son, ‘Let us make man in our image and our likeness’ [Gen. 1:26]? Or when he reads [as having been said] to Christ: ‘Thou art my Son, this day have I begotten you. Ask of me, and I will give you the heathens for your inheritance, and the ends of the earth for your possession’ [Ps. 2:7–8]? Or when also that beloved writer says: ‘The Lord said unto my Lord, Sit thou on my right hand, until I shall make your enemies the stool of your feet’ [Ps. 110:1]? Or when, unfolding the prophecies of Isaiah, he finds it written thus: ‘Thus says the Lord to Christ my Lord’? Or when he reads: ‘I came not down from heaven to do mine own will, but the will of him that sent me’ [John 6:38]? Or when he finds it written: ‘Because he who sent me is greater than I’ [cf. John 14:24, 28]? Or when he finds it placed side by side with others: ‘Moreover, in your law it is written that the witness of two is true. I bear witness of myself, and the Father who sent me bears witness of me’ [cf. John 8:17–18]?” (Treatise on the Trinity 26 [A.D. 235]). - Novatian

“See, in short you have it that the Father is one, the Son another, and the Holy Spirit another; in person, each is other, but in nature they are not other. In this regard he [Christ] says, ‘The Father and I, we are one’ [John 10:30]. He teaches us that ‘one’ refers to their nature and ‘we are’ to their persons. In like manner it is said, ‘There are three who bear witness in heaven, the Father, the Word, and the Spirit, and these three are one’ [cf. 1 John 5:7]. Let Sabellius hear ‘we are,’ let him hear ‘three,’ and let him believe that there are three persons” (The Trinity 4:1 [A.D. 513]). - Fulgentius of Ruspe

“They [the Father and the Son] are one, not as one thing now divided into two, but really constituting only one, nor as one thing twice named, so that the same becomes at one time the Father and at another his own Son. This latter is what Sabellius held, and he was judged a heretic. On the contrary, they are two, because the Father is Father and is not his own Son, and the Son is Son and not his own Father” (Discourses Against the Arians 3:4 [A.D. 360]). - Athansius

“Next, then, I may properly turn to those who divide and cut apart and destroy the monarchy, the most sacred proclamation of the Church of God, making of it, as it were, three powers, distinct substances, and three godheads. I have heard that some of your catechists and teachers of the divine Word take the lead in this tenet. They are, so to speak, diametrically opposed to the opinion of Sabellius. He, in his blasphemy, says that the Son is the Father and vice versa” (Letters of Pope Dionysius to Bishop Dionysius of Alexandria 1:1 [A.D. 262]). - Pope Dionysius