38 Dativus of Badiæ said "We, so far as lies within our power, refuse to communicate with a heretic, unless he has been baptized in the Church, and received remission of his sins."
39. The answer to this is: If your reason for wishing him to be baptized is that he has not received remission of sins, supposing you find a man within the Church who has been baptized, though entertaining hatred towards his brother, since the Lord cannot lie, who says, "If you forgive not men their trespasses, neither will your Father forgive your trespasses," will you bid such an one, when corrected, to be baptized afresh? Assuredly not; so neither should you bid the heretic. It is clear that we must not pass unnoticed why he did not briefly say, "We do not communicate with a heretic," but added, "so far as lies within our power." For he saw that a greater number agreed with this view, from whose communion, however, he and his friends could not separate themselves, lest unity should be impaired, and so he added, "so far as lies within our power,"— showing beyond all doubt that he did not willingly communicate with those whom he held to be without baptism, but that yet all things were to be endured for the sake of peace and unity; just as was done also by those who thought that Dativus and his party were in the wrong, and who held what afterwards was taught by a fuller declaration of the truth, and urged by ancient custom, which received the stronger confirmation of a later Council; yet in turn, with anxious piety, they showed toleration towards each other, though without violation of Christian charity they entertained different opinions, endeavoring to keep the unity of the Spirit in the bond of peace, till God should reveal to one of them, were he otherwise minded, even this error of his ways. And to this I would have those give heed, by whom unity is attacked on the authority of this very Council by which it is declared how much unity should be loved.
Source: On Baptism, Against the Donatists (New Advent)