Plutarch De fraterno amore 10

[10] Only after the erring brother has been defended in this manner should the other turn to him and rebuke him somewhat sharply, pointing out with all frankness his errors of commission and of omission. For one should neither give free rein to brothers, nor, again, should one trample on them when they are at fault (for the latter is the act of one who gloats over the sinner, the former that of one who aids and abets him), but should apply his admonition as one who cares for his brother and grieves with him. Otherwise he who has been the most zealous advocate before his parents becomes before the brother himself the most vehement of accusers. But if a brother is guiltless when he is accused, though it is right to be subservient to parents in everything else and to endure all their wrath and displeasure, yet pleas and justifications offered to parents on behalf of a brother who is being undeservedly criticized or punished are honourable and not reprehensible; nor must one be afraid that the words of Sophocles ¹ will be addressed to him: when one is speaking with all frankness on behalf of a brother who seems to be receiving unfair treatment. For to the parents themselves, when they are proved wrong, such a litigation makes defeat sweeter than victory.