24 Nor let any one think that, because baptism is proposed to them, heretics will be kept back from coming to the Church, as if offended at the name of a second baptism; nay, but on this very account they are rather driven to the necessity of coming by the testimony of truth shown and proved to them. For if they shall see that it is determined and decreed by our judgment and sentence, that the baptism wherewith they are there baptized is considered just and legitimate, they will think that they are justly and legitimately in possession of the Church also, and the other gifts of the Church; nor will there be any reason for their coming to us, when, as they have baptism, they seem also to have the rest.
But further, when they know that there is no baptism without, and that no remission of sins can be given outside the Church, they more eagerly and readily hasten to us, and implore the gifts and benefits of the Church our Mother, assured that they can in no wise attain to the true promise of divine grace unless they first come to the truth of the Church. Nor will heretics refuse to be baptized among us with the lawful and true baptism of the Church, when they shall have learned from us that they also were baptized by Paul, who already had been baptized with the baptism of John, as we read in the Acts of the Apostles.
Source: The Epistles of Cyprian (New Advent)