22 "For as regards the fact that to preserve the figure of unity the Lord gave the power to Peter that whatsoever he should loose on earth should be loosed," it is clear that that unity is also described as one dove without fault. Can it be said, then, that to this same dove belong all those greedy ones, whose existence in the same Catholic Church Cyprian himself so grievously bewailed? For birds of prey, I believe, cannot be called doves, but rather hawks. How then did they baptize those who used to plunder estates by treacherous deceit, and increase their profits by compound usury, if baptism is only given by that indivisible and chaste and perfect dove, that unity which can only be understood as existing among the good?
Is it possible that, by the prayers of the saints who are spiritual within the Church, as though by the frequent lamentations of the dove, a great sacrament is dispensed, with a secret administration of the mercy of God, so that their sins also are loosed who are baptized, not by the dove but by the hawk, if they come to that sacrament in the peace of Catholic unity? But if this be so, why should it not also be the case that, as each man comes from heresy or schism to the Catholic peace, his sins should be loosed through their prayers?
But the integrity of the sacrament is everywhere recognized, though it will not avail for the irrevocable remission of sins outside the unity of the Church. Nor will the prayers of the saints, or, in other words, the groanings of that one dove, be able to help one who is set in heresy or schism; just as they are not able to help one who is placed within the Church, if by a wicked life he himself retain the debts of his sins against himself, and that though he be baptized, not by this hawk, but by the pious ministry of the dove herself.
Source: On Baptism, Against the Donatists (New Advent)