67 Castus of Sicca said: He who presumes to follow custom in despite of truth is either envious and evilly disposed towards the brethren to whom the truth is revealed, or else he is ungrateful towards God, by whose inspiration His Church is instructed."
68. If this man proved that those who differed from him, and held the view that has since been held by the whole world under the sanction of a Christian Council, were following custom so as to despise truth, we should have reason for fearing these words; but seeing that this custom is found both to have had its origin in truth and to have been confirmed by truth, we have nothing to fear in this judgment. And yet, if they were envious or evilly disposed towards the brethren, or ungrateful towards God, see with what kind of men they were willing to hold communion; see what kind of men, holding different opinions from their own, they treated as Cyprian enjoined them at the first, not removing them from the right of communion; see by what kind of men they were not polluted in the preservation of unity; see how greatly the bond of peace was to be loved; see what views they hold who bring charges against us, founded on the Council of bishops, their predecessors, whose example they do not imitate, and by whose example, when the rights of the case are considered, they are condemned. If it was the custom, as this judgment bears witness, that heretics coming to the Church should be received with the baptism which they already had, either this was done rightly, or the evil do not pollute the good in unity. If it was rightly done, why do they accuse the world because they are so received? But if the evil do not pollute the good in unity, how do they defend themselves against the charge of sacrilegious separation?
Source: On Baptism, Against the Donatists (New Advent)