Augustine of Hippo
Catena Aurea · Matthäusevangelium 18
Moreover if thy brother shall trespass against thee, go and tell him his fault between thee and him alone: if he shall hear thee, thou hast gained thy brother. But if he will not hear thee, then take with thee one or two more, that in the mouth of two or three witnesses every word may be established. And if he shall neglect to hear them, tell it unto the Church: but if he neglect to hear the Church, let him be unto thee as an heathen man and a Publican.
(de Civ. Dei, i. 9.) For often we wrongly shun to teach and admonish, or to rebuke and check the wicked, either because the task is irksome, or because we would escape their enmity, lest they should harm or obstruct us in temporal things, whether in gaining objects we desire, or in holding what our frailty fears to love. But if any one spares reproof of evil doers, because he seeks fitter occasion, or fears to make them worse, or that they may be an impediment to the good and pious living of other weak ones, or may grieve them, or turn them from the faith; herein there is seen no considerations of covetousness, but the prudence of charity. And much weightier reason have they who are set over the churches, to the end they should not spare to rebuke sin; though not even he is free from this blame, who, though not in authority, wots of many things in them to whom he is bound by the ties of this life, which should be touched by admonition or correction, but neglects to do so; shunning their displeasure on account of things which he does not unduly use in this life, but wherewith he is unduly delighted.