8 Between us, then, and what we may call the genuine Donatists, whose bishop is Primianus at Carthage, there is now no controversy on this point. For God willed that it should be ended by means of the followers of Maximianus, that they should be compelled by the precedent of his case to acknowledge what they would not allow at the persuasion of Christian charity. But this brings us to consider next, whether those men do not seem to have something to say for themselves, who refuse communion with the party of Primianus, contending that in their body there remains greater sincerity of Donatism, just in proportion to the paucity of their numbers.
And even if these were only the party of Maximianus, we should not be justified in despising their salvation. How much more, then, are we bound to consider it, when we find that this same party of Donatus is split up into many most minute fractions, all which small sections of the body blame the one much larger portion which has Primianus for its head, because they receive the baptism of the followers of Maximianus; while each endeavors to maintain that it is the sole receptacle of true baptism, which exists nowhere else, neither in the whole of the world where the Catholic Church extends itself, nor in that larger main body of the Donatists, nor even in the other minute sections, but only in itself.
Whereas, if all these fragments would listen not to the voice of man, but to the most unmistakable manifestation of the truth, and would be willing to curb the fiery temper of their own perversity, they would return from their own barrenness, not indeed to the main body of Donatus, a mere fragment of which they are a smaller fragment, but to the never-failing fruitfulness of the root of the Catholic Church. For all of them who are not against us are for us; but when they gather not with us, they scatter abroad.
Source: On Baptism, Against the Donatists (New Advent)