Is it permissible for a person to judge another as having committed a sin?

Declaring a Muslim an infidel (takfir) is a serious matter and a grave error that is impermissible. Whoever calls a man an infidel, it rebounds upon him. Regarding takfir for abandoning prayer, there is detail and disagreement. A person assaulting a guard is not in line with Muslim ethics, except in self-defense. Denying hatred of Arabs is correct, for among them are those who do good and those who do evil, and hating them absolutely indicates no good. As for whoever curses Arabs and claims he meant only the unjust among them, he should be disciplined. If he did not make such a claim, he should be executed.