Sahih Muslim Book 4, Hadith Number 2073.

Chapter : The dead who is praised in good words, or who is condemned in bad words.

Anas b. Malik reported: There passed a bier (being carried by people) and it was lauded in good terms. Upon this the Apostle of Allah (may peace be upon him) said: It has become certain, it has become certain, it has become certain. And there passed a bier and it was condemned in bad words. Upon this the Apostle of Allah (may peace be upon him) said: It has become certain, it has become certain, it has become certain. ‘Umar said: May my father and mother be ransom for you ! There passed a bier and it was praised in good terms, and you said: It has become certain, it has become certain, it has become certain. And there passed a bier and it was condemned in bad words, and you said: It has become certain, it has become certain, it has become certain. Upon this the Messenger of Allah (way peace be upon him) said: He whom you praised in good terms, Paradise has become certain for him, and he whom you condemned in bad words, Hell has become certain for him. You are Allah’s witnesses in the earth, you are Allah’s witnesses in the earth, you are Allah’s witnesses in the earth.