Ante-Nicene Fathers Volume 5
Cyprian: Epistle LXXV
Starting with (again) the question of baptism by heretics, this Epistle returns to the question of Novatian and even touches on the question of the proper method of baptism. Much of this Epistle can be skimmed (especially the beginning), as it simply repeats Cyprian's claim that baptism by heretics doesn't count because they are not a part of the "true" church. Here he ups the claim a bit by saying that merely leaving the church or causing a schism is enough, even if there's not specifically an active heresy. As evidence for this Cyprian points to sayings (yes, slightly out of context) from Jesus (Luke 21:23) and John (1 John 2:18-19). "For the faith of the sacred Scripture sets forth that the church is not without, nor can be separated nor divided against itself, but maintains the unity of an inseparable and undivided house." As we've repeatedly seen, the issue here is one of confusion of the visible church with the invisible church.
That said, when it comes to the method of baptism, Cyprian returns to the position of extreme charity. Those who are sick or weak, for example, may be sprinkled without troubling the conscience of anyone involved. After all, what matters is the "full and entire faith both of the giver and the receiver." What happens with water is merely an external reflection of the internal spiritual reality (which for Cyprian is simultaneous, while in Scripture the latter follows the former). Nor should we get too uptight about the name of it, some have called Christians who are sprinkled "Clinics", since they were baptized irregularly. We, however, shouldn't care so long as they are baptized in faith and properly. We must not think of them as being lesser believers or having less of the Holy Spirit or any such thing. Mercy and generosity in all! Again, there's far too much baptismal regeneration here, but the last few paragraphs are at least worth skimming.