What is the ruling on someone who spoke about a brother who wronged his mother?

A Muslim must guard his tongue, for whoever believes in Allah and the Last Day should speak good or remain silent. If someone wrongs the questioner's mother, it is permissible to respond truthfully without lying, for the Messenger of Allah, peace and blessings be upon him, said: "The two who revile each other, what they say is upon the one who initiated it, unless the wronged party transgresses." It is also permissible to mention his actions to whomever one complains to, in order to repel injustice. However, if a person wrongs his mother, the duty is to advise him and warn him against disobedience to parents (Uquq al-Walidayn), and to command him to treat his parents with kindness. The general principle is to prevent defamation of someone who has done wrong if they are not openly defiant, based on the Prophet's saying, peace and blessings be upon him: "Whoever conceals a Muslim's fault, Allah will conceal his fault in this world and the Hereafter." However, it is permissible to mention him for the purpose of warning against him if he is openly defiant.