Firmilian of Caesarea, Letter to Cyprian (Ep. 74/75) 7
You have also given a strong answer on that point where Stephen wrote in his letter that heretics themselves agree on baptism and that they do not rebaptize those who come to them from other groups but simply admit them to communion, as if we ought to do the same. You have already shown how ridiculous it is to follow those who err, yet we add this further observation: it is no surprise that heretics act this way. Although they disagree on minor points, they share one fundamental consensus — they blaspheme the Creator by inventing dreams and phantasms of an unknown God. It follows naturally that they would agree on the emptiness of their baptism just as they agree on rejecting the truth of God.
Since it would take too long to answer each of their wicked or pointless claims individually, it is enough to state the matter briefly: those who do not hold the true Lord as Father cannot hold the truth of the Son or of the Holy Spirit. This applies equally to those called Cataphrygians, who claim new prophecies — they can possess neither the Father nor the Son nor the Holy Spirit. If we ask which Christ they preach, they answer that they preach the one who sent the Spirit to speak through Montanus and Prisca. When we see that the spirit at work in them is not the Spirit of truth but a spirit of error, we recognize that those who defend their false prophecy against the faith of Christ cannot have Christ.
Every other heretic who has cut himself off from the Church of God can possess no power or grace, because all power and grace are established in the Church, where elders preside and hold the authority to baptize, lay on hands, and ordain. Just as a heretic is not permitted to ordain or lay on hands, so he is not permitted to baptize or perform anything holy or spiritual, since he is alien to the spiritual and deifying sanctity that belongs to the Church. We confirmed this entire position long ago at Iconium in Phrygia, when bishops gathered from Galatia, Cilicia, and the surrounding regions and resolved to uphold and defend it firmly against heretics, because some were doubting this matter.
Latin
Sed et ad illam partem bene a vobis responsum est ubi Stephanus in epistola sua dixit « haereticos quoque ipsos in baptismo convenire, et quod alterutrum ad se venientes non baptizent, sed communicent tantum, » quasi et nos hoc facere debeamus. Quo in loco, etsi vos jam probastis satis ridiculum esse ut quis sequatur errantes, illud tamen ex abundanti addimus, non esse mirum si sic haeretici agant, qui, etsi in quibusdam minoribus discrepant, in eo tamen, quod est maximum, unum et eumdem consensum tenent ut blasphement Creatorem, quaedam somnia sibi et phantasmata ignoti Dei confingentes; quos utique consequens est sic consentire in baptismi sui vanitate ut consentiunt in repudianda divinitatis veritate. De quibus, quoniam longum est ad singula eorum vel scelesta vel supervacua respondere satis est breviter illud in compendio dicere, eos qui non teneant verum Dominum, Patrem, tenere non posse nec Filii nec Spiritus sancti veritatem, secundum quod etiam illi qui Cataphrygae appellantur, et novas prophetias usurpare conantur, nec Patrem possunt habere nec Filium nec [Spiritum sanctum]; a quibus si quaeramus quem Christum praedicent, respondebunt eum se praedicare qui miserit Spiritum per Montanum et Priscam locutum. In quibus cum animadvertamus non veritatis Spiritum sed erroris fuisse, cognoscimus eos qui falsam illorum prophetiam contra Christi fidem vindicant Christum habere non posse. Sed et caeteri quique haeretici, si se ab Ecclesia Dei sciderint, nihil habere potestatis aut gratiae possunt, quando omnis potestas et gratia in Ecclesia constituta sit, ubi praesident majores natu, qui et baptizandi et manum imponendi et ordinandi possident potestatem. Haeretico enim, sicut ordinare non licet nec manum imponere, ita nec baptizare nec quicquam sancte nec spiritaliter gerere, quando alienus sit a spiritali et deifica sanctitate. Quod totum nos jampridem in Iconio, qui Phrygiae locus est, collecti in unum convenientibus ex Galatia et Cilicia et caeteris proximis regionibus, confirmavimus tenendum contra haereticos firmiter et vindicandum, cum a quibusdam de ista re dubitaretur.