What is the ruling concerning a Muslim who rejoiced when his oppressive brother was punished in this worldly life, and is he sinful for that?

The oppressed person has three choices regarding their oppressor: forgiving them in hope of reward, not forgiving them so that the oppressor may be punished, or taking their right by reciprocating the evil with its like. The best of these is forgiveness. As for malice, hatred, and gloating over someone's misfortune, these are not the manners of a Muslim. He should remember the words of Allah Almighty: "And let them pardon and overlook. Would you not like that Allah should forgive you? And Allah is Forgiving and Merciful." If a Muslim is unable to overcome what he feels within himself after forgiving, then we hope there is no sin upon him as long as he does not act or speak.