Firmilian of Caesarea, Letter to Cyprian 5
Because the legate you sent was eager to return to you and the winter season pressed upon us, we have answered your letters in writing as fully as we could.
Regarding what Stephanus claimed — that the Apostles forbade the baptism of those coming from heresy and handed down this rule for posterity — you have replied most completely that no one is so foolish as to believe the Apostles delivered such a thing; for the heresies themselves are known to be detestable and execrable, having arisen later, when Marcion, a disciple of Cerdon, appeared long after the Apostles and after a long interval from them and introduced a sacrilegious tradition against God; Apelles, agreeing with his blasphemy, added many other new and graver doctrines hostile to faith and truth.
Moreover, the time of Valentinus and Basilides is clear: they too, after the Apostles and after a long age, rebelled against the Church of God with their wicked lies.
The other heretics are likewise known to have introduced their depraved sects and perverse inventions afterward, each as he was led by error; all of them are manifestly self‑condemned, having pronounced an inexcusable sentence against themselves before the day of judgment; whoever confirms the baptism of such persons does nothing other than adjudicate himself alongside them and condemn himself by making himself a participant in such things.
Latin
Quoniam vero legatus iste a vobis missus regredi ad vos festinabat, et hibernum tempus urgebat, quantum potuimus ad scripta vestra rescripsimus. Et quidem, quantum ad id pertineat quod Stephanus dixit, quasi Apostoli eos qui ab haeresi veniunt baptizari prohibuerint et hoc custodiendum posteris tradiderint, plenissime vos respondistis neminem tam stultum esse qui hoc credat Apostolos tradidisse, quando etiam ipsas haereses constet execrabiles ac detestandas postea exstitisse, cum et Marcion, Cerdonis discipulus, inveniatur sero post Apostolos et post longa ab eis tempora sacrilegam adversus Deum traditionem induxisse; Apelles quoque, blasphemiae ejus consentiens, multa alia nova et graviora fidei ac veritati inimica addiderit. Sed et Valentini et Basilidis tempus manifestum est, quod et ipsi, post Apostolos et post longam aetatem, adversus Ecclesiam Dei sceleratis mendaciis suis rebellaverint. Caeteros quoque haereticos constat pravas suas sectas et inventiones perversas, prout quisque errore ductus est, postea induxisse; quos omnes manifestum est a semetipsis damnatos esse, et ante diem judicii inexcusabilem sententiam adversus semetipsos dixisse: quorum baptisma qui confirmat, quid aliud quam cum ipsis se adjudicat, et se ipse participem talibus faciendo condemnat.