30 Secundinus of Cedias said: "Since our Lord Christ said, 'He that is not with me is against me,' and the Apostle John declares those who go out from the Church to be antichrists, without all doubt the enemies of Christ, and those who are called antichrists, cannot minister the grace of the baptism which gives salvation; and therefore my judgment is that those who take refuge in the Church from the snares of heresy should be baptized by us, who of His condescension are called the friends of God."
31. The answer to which is, That all are the opponents of Christ, to whom, on their saying, "Lord, have we not in Your name done many wonderful things?" with all the rest that is there recorded, He shall at the last day answer, "I never knew you: depart from me, you that work iniquity," — all which kind of chaff is destined for the fire, if it persevere to the last in its wickedness, whether any part of it fly outside before its winnowing, or whether it seem to be within. If, therefore, those heretics who come to the Church are to be again baptized, that they may be baptized by the friends of God, are those covetous men, those robbers, murderers, the friends of God, or must those whom they have baptized be baptized afresh?
Source: On Baptism, Against the Donatists (New Advent)