16 But Cyprian was right in not being moved by what Jubaianus wrote, that "the followers of Novatian rebaptize those who come to them from the Catholic Church." For, in the first place, it does not follow that whatever heretics have done in a perverse spirit of mimicry, Catholics are therefore to abstain from doing, because the heretics do the same. And again, the reasons are different for which heretics and the Catholic Church ought respectively to abstain from rebaptizing.
For it would not be right for heretics to do so, even if it were fitting in the Catholic Church; because their argument is, that among the Catholics is wanting that which they themselves received while still within the pale, and took away with them when they departed. Whereas the reason why the Catholic Church should not administer again the baptism which was given among heretics, is that it may not seem to decide that a power which is Christ's alone belongs to its members, or to pronounce that to be wanting in the heretics which they have received within her pale, and certainly could not lose by straying outside.
For thus much Cyprian himself, with all the rest, established, that if any should return from heresy to the Church, they should be received back, not by baptism, but by the discipline of penitence; whence it is clear that they cannot be held to lose by their secession what is not restored to them when they return. Nor ought it for a moment to be said that, as their heresy is their own, as their error is their own, as the sacrilege of disunion is their own, so also the baptism is their own, which is really Christ's. Accordingly, while the evils which are their own are corrected when they return, so in that which is not theirs His presence should be recognised, from whom it is.
Source: On Baptism, Against the Donatists (New Advent)