11 Cæcilius of Bilta said: "I know of one baptism in the one Church and of none outside the Church. The one will be where there is true hope and sure faith. For so it is written, 'One faith, one hope, one baptism.' Not among heretics, where there is no hope and a false faith; where all things are done by a lie; where one possessed of a devil exorcises; the question of the sacrament is asked by one from whose mouth and words proceeds a cancer; the faithless gives faith; the guilty gives pardon for sins and Antichrist baptizes in the name of Christ; one accursed of God blesses; the dead promises life; the unpeaceful gives peace; the blasphemer calls on God; the profane administers the priesthood; the sacrilegious sets up the altar. To all this is added this further evil that the servant of the devil dares to celebrate the eucharist. If this be not so, let those who stand by them prove that all of it is false concerning heretics. See the kind of things to which the Church is compelled to assent, being forced to communicate without baptism or the remission of sins. This, brethren, we ought to shun and avoid, separating ourselves from so great a sin, and holding to the one baptism which is granted to the Church alone."
12. To this I answer, that all who even within the Church profess that they know God, but deny Him in their deeds, such as are the covetous and envious, and those who, because they hate their brethren, are pronounced to be murderers, not on my testimony, but on that of the holy Apostle John, — all these are both devoid of hope, because they have a bad conscience; and are faithless, because they do not do what they have vowed to God; and liars, because they make false professions; and possessed of devils, because they give place in their heart to the devil and his angels; and their words work corruption, since they corrupt good manners by evil communications; and they are infidels, because they laugh at the threats which God utters against such men; and accursed, because they live wickedly; and antichrists, because their lives are opposed to Christ; and cursed of God, since holy Scripture everywhere calls down curses on such men; and dead, because they are without the life of righteousness; and unpeaceful, because by their contrary deeds they are at variance with God's behests; and blasphemous, because by their abandoned acts despite is done to the name of Christian; and profane, because they are spiritually shut out from that inner sanctuary of God; and sacrilegious, because by their evil life they defile the temple of God within themselves; and servants of the devil, because they do service to fraud and covetousness, which is idolatry. That of such a kind are some, nay very many, even within the Church, is testified both by Paul the apostle and by Cyprian the bishop. Why, then, do they baptize? Why also are some, who "renounce the world in words and not in deeds," baptized without being converted from a life like this, and not rebaptized when they are converted? And as to what he says with such indignation, "See the kind of things to which the Church is compelled to assent, being forced to communicate without baptism or the remission of sins," he could never have used such expressions had there not been the other bishops who elsewhere forced men to such things. Whence also it is shown that at that time those men held the truer views who did not depart from the primitive custom, which is since confirmed by the consent of a general Council. But what does he mean by adding, "This, brethren, we ought to shun and avoid, separating ourselves from so great a sin?" For if he means that he is not to do nor to approve of this, that is another matter; but if he means to condemn and sever from him those that hold the contrary opinion, he is setting himself against the earlier words of Cyprian, "Judging no man, nor depriving any of the right of communion if he differ from us."
Source: On Baptism, Against the Donatists (New Advent)