Jerome
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.
Or it is to be understood in this way; If he will not hear thee, take with thee one brother only; if he yet will not hear, take a third, either from your zeal for his amendment, that shame or admonition may move him; or for the purpose of meeting before witnesses.