Anas (May Allah be pleased with him) reported: Some Companions happened to pass by a funeral procession (bier) and they praised him (the deceased). The Prophet (PBUH) said, "he will certainly enter it.'' Then they passed by another funeral procession and they spoke ill of the deceased. The Prophet (PBUH) said, "He will certainly enter it.'' `Umar bin Al-Khattab (May Allah be pleased with him) said: "(O Messenger of Allah,) what do you mean by `He will certainly enter it?'' He (PBUH) replied, "You praised the first person, so he will enter Jannah; and you spoke ill of the second person, so he will enter Hell. You are Allah's witnesses on earth.''
[Al-Bukhari and Muslim].

Commentary: The remarks of true believers reflect their righteousness and integrity of character. If they bear witness to the purity of heart of a man, he is sure to go to Jannah. And if they comment on the evil-mindedness of somebody, he is likely to be consigned to Hell-fire. Indeed, a believer never utters anything out of malice or self-conceit. There are some Ahadith which forbid us to speak ill of dead people. This rule applies to the true believers only. The Shari`ah argument is against it. However, we are allowed to talk about the misdeeds of the infidels and people who commit sins openly, disregarding the Shari`ah so that others may abstain from imitating a bad example.