Praise be to Allaah.  

Firstly:  

The Muslim has to guard his tongue and avoid things that have been forbidden. Among these forbidden things which people take often lightly are gheebah (backbiting), buhtaan (slander) and nameemah (malicious gossip). 

Gheebah or backbiting means speaking about a Muslim in his absence and saying things that he would not like to have spread around or mentioned. Buhtaan or slander means saying things about a Muslim that are not true, or in other words telling lies about him. Nameemah or malicious gossip means telling one person what another said in order to cause trouble between them. 

There is a great deal of evidence to show that these actions are haraam. It will suffice for us to mention just a few of them in order to demonstrate that they are haraam. 

Allaah 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 (so hate backbiting). And fear Allaah. Verily, Allaah is the One Who forgives and accepts repentance, Most Merciful”

[al-Hujuraat 49:12] 

It was narrated from Abu Hurayrah (may Allaah be pleased with him) that the Messenger of Allaah SAWS (peace and blessings of Allaah be upon him) said: “Do you know what gheebah (backbiting) is?” They said, “Allaah and His Messenger know best.” He said, “Saying something about your brother that he dislikes.” It was said, “What if what I say about my brother is true?” He said, “If what you say is true then you have backbitten about him, and if it is not true, then you have slandered him.” 

Narrated by Muslim, 2589 

It was narrated that Ibn ‘Abbaas said: The Messenger of Allaah (peace and blessings of Allaah be upon him) passed by two graves and said, “They are being punished, but they are not being punished for anything that was difficult to avoid. One of them used to walk about spreading malicious gossip (nameemah), and the other used not to take precautions to avoid getting urine on himself when he urinated.” Then he called for a green branch, which he split in two and planted a piece on each grave, and said, “May their torment be reduced so long as these do not dry out.” 

Narrated by al-Bukhaari, 213; Muslim, 292 

For a person to say of another, “He cannot control his tongue (or he has a loose tongue)” is undoubtedly one of those things that a person would dislike to have said about him. If it is true, then it is gheebah (backbiting), and if it is not true then it is buhtaan (slander). 

Everyone who does any kind of backbiting, slander or malicious gossip has to repent and pray for forgiveness, and that is between him and Allaah. If he knows that any of his words reached the person about whom he was speaking, then he should go to him and ask him to forgive him. But if he does not know, then he should not tell him; rather he should pray for forgiveness for him and make du’aa’ for him, and speak well of him in his absence just as he spoke against him. Similarly, if he knows that telling him will provoke more enmity, then it is sufficient to make du’aa’ for him, speak well of him and pray for forgiveness for him. 

It was narrated that Abu Hurayrah (may Allaah be pleased with him) said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Whoever has wronged his brother with regard to his honour or anything else, let him seek his forgiveness today, before there will be no dinar and no dirham, and if he has any good deeds to his credit they will be taken from him in a manner commensurate with the wrong he did, and if he has no good deeds, then some of his counterpart’s bad deeds will be taken and added to his burden.” 

Narrated by al-Bukhaari, 2317. 

Shaykh al-Islam Ibn Taymiyah said: 

Whoever wrongs a person by slandering him, backbiting about him or insulting him, then repents, Allaah will accept his repentance, but if the one who was wronged finds out about that, he has the right to settle the score. But if he slandered him or backbit about him and the person did not hear of that, then there are two views according to the scholars, both of which were narrated from Ahmad, the more correct of which is that he should not tell him that he spoke against him in his absence. It was said that he should rather speak well of him in his absence just as he spoke badly of him in his absence, as al-Hasan al-Basri said: the expiation for gheebah is to pray for forgiveness for the person about whom you backbit.

 Majmoo’ al-Fataawa, 3/291

 And Allaah knows best.