From Ibn 'Umar (radiyallaahu 'anhumaa) who said that Allaah's Messenger (salallaahu 'alaihi wa'sallam) said:
Whoever intercedes and prevents one of the punishments prescribed by Allaah, the Mighty and Majestic, then he has opposed Allaah regarding His orders. Whoever dies with a debt due on him then it will not be repaid by deenaars and dirhams but rather by good and bad deeds. Whoever disputes for something which he knows is false then he remains in Allaah's anger until he desists. Whoever accuses a believer of something that is untrue then Allaah will make him dwell in the pus flowing from the inhabitants of the Fire and he will not leaver until he retracts from what he said.
So the lethal plague of backbiting destroys one's good deeds, destroys brotherhood and destroys one's reward. So the true Muslim does not backbite, nor does he allow backbiting to take place in his presence. So let those people fear Allaah, those whose bodies do not develop and those whose spirit is not fed except upon spreading rumours and inventing lies against the servants of Allaah claiming that 'this is for the benefit of da'wah!'
How strange! What benefit to the da'wah will be achieved through slandering, backbiting and mentioning bad manners to others? Do you think, O you who backbites the people, that you are far removed form defect? O you who can only see the deficiencies of others, do you think that you are free from any mistakes? '...rather you are full of deficiencies and the people have tongues!' Also from those things which must be known is that: