Gossip and backbiting:

The Prophet (peace and blessings of Allaah be upon him) explained the meaning of this aayah. He said: “Do you know whatgheebah (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).

(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).

Slander

Some people go about repeating the words of others to cause trouble between people; this is one of the greatest causes of broken relations and stirring up feelings of hatred among people. Allaah condemned the one who does this (interpretation of the meaning): "And obey not everyone who swears much, - and is considered worthless, a slanderer, going about with calumnies." [al-Qalam 68:10-11]

Hudhayfah reported that the Prophet (peace and blessings of Allaah be upon him) said: "No eavesdropper will enter Paradise."(Reported by al-Bukhaari, see al-Fath, 10/472; "eavesdropper" here refers to a person who eavesdrops on others without their knowing, then goes and tells others what he has heard)

Ibn 'Abbaas said: "The Prophet (peace and blessings of Allaah be upon him) passed by one of the gardens of Madeenah, and heard the sound of two people being punished in their graves. The Prophet (peace and blessings of Allaah be upon him) said: "They are being punished, but they are not being punished for any major sin; one of them used never to clean himself properly after urinating, and the other used to spread malicious slander . . ." (Reported by al-Bukhaari; see Fath al-Baari, 1/317).

One of the worst forms of this sin is to cause trouble between a husband and wife, or vice versa, or to tell one's boss what other employees are saying, in order to create trouble. All of this is haraam..