1560. Abu Dharr (May Allah be pleased with him) reported: I heard the Messenger of Allah (sallallaahu ’alayhi wa sallam) saying, “When any Muslim accuses another Muslim of sin or of disbelief, the reproach rebounds upon the one who utters it, if the other person is not deserving of it.”
Commentary: What this Hadith stresses is that one should never say about a Muslim that he is sinful (Fasiq) or disbeliever (Kafir) when he is not so. The reason is that in that case, one who says it, will be held Fasiq or Kafir. One should, therefore, strictly refrain from uttering such statements.