Gossip and backbiting:

Many gatherings produce nothing but gossip about other Muslims and slander of their honour. This is something which Allaah has forbidden His slaves, and has drawn the most repulsive analogy to put them off. He says (interpretation of the meaning): “. . . neither backbite one another. Would one of you like to eat the flesh of his dead brother? You would hate it . . .” [al-Hujuraat 49:12]
The Prophet (peace and blessings of Allaah be upon him) explained the meaning of this aayah. He said: “Do you know what gheebah (gossip or backbiting) is?” They said, “Allaah and His Messenger know best.” He said: "To say something about your brother that he does not want to be said." He was asked, "What do you think if what is said about him is true?" He said, "If what you say about him is true, this is backbiting, and if what you say about him is not true, this is a lie." (Reported by Muslim, 4/2001).
Gossip or backbiting means saying something about a Muslim which may be true but which he does not like to hear spoken, whether it be about his physical appearance, his adherence to religion, his worldly affairs, his self, his behaviour or his character. There are many forms of gossip, including talking about a person's faults and imitating him to make fun of him.
People take the matter of gheebah very lightly, although it is very serious in the sight of Allaah, as is indicated by the words of the Prophet (peace and blessings of Allaah be upon him): "There are seventy-two forms of riba, the least of which is as bad as a man having intercourse with his own mother, and the worst of which is when a man slanders the honour of his brother." (Silsilah al-Saheeh, 1871).
Whoever is present in a gathering where gossip takes place should "forbid what is evil" and defend his absent brother. The Prophet (peace and blessings of Allaah be upon him) encouraged us to do this when he said: "Whoever defends the honour of his Muslim brother, Allaah will protect his face from the Fire on the Day of Resurrection." (Reported by Ahmad, 6/450; see also Saheeh al-Jaami', 6238).