If someone, God forbid, has been guilty of this ugly act, he or she must purge this vice and nourish the roots of sincerity, unity, and solidarity in his or her heart by following these steps:
Meditate for a while about the effects of this sin in this world and in the Hereafter. Reflect on the fearsome, frightful forms that will beset you in the grave, in the Barzakh, and on the Day of Resurrection. Heed the words of the Holy Prophet (s) and his household (‘a) for their pearls of wisdom in this regard will overwhelm you. Then weigh a quarter of an hour's pleasantries, gossip, and satisfaction of the imaginative lust against thousands upon thousands of years of adversity or eternal damnation in hell and everlasting painful chastisement!
Consider this: even if you have enmity toward a person whom you backbite, that animosity requires that you should not resort to backbiting. It is stated in the traditions that the good deeds of the backbiter are transferred to the book of deeds of the victim of his backbiting, and the victim's sins are transferred to the record of the backbiter.
Repent and seek the forgiveness of the victim, if this is possible without any chance of vicious consequences; otherwise, you must implore God's mercy for the victim.
Gather all your strength to rid your soul of this sin at all cost, by making a covenant with yourself to abstain from this abominable for a certain time. Bring your tongue under control and be fully watchful of yourself, steadfastly vigilant, calling yourself to account. God willing, it is hoped that after some time you will find yourself reformed and free of its ill traces. Gradually the burden of the task will ease, and you will feel a natural disposition to dislike and detest it. At that point, you will come to possess spiritual peace and delight in achieving freedom from this vice.
Backbiting often results from a weakness in the backbiter’s own soul, such as an inferiority complex. You should pry into your soul to discover what weakness prompted you to backbite your brother or sister; then set out to remedy the weakness.
The Prophet (s) said: "No fire is faster in consuming dry wood than gheebah in consuming a devotee's virtues." [Al-Mahajjat al-bayda', vol. 5, p. 264]
... Nor backbite one another; would any of you like to eat the flesh of his dead brother? You would abhor it.
Prophet Muhammad (s) once said to Imam ‘Ali (‘a): “O ‘Ali! When someone hears the backbiting of his Muslim brother committed in his presence, yet he does not rally to his assistance despite being capable of doing so, God shall humiliate him in the world and in the Hereafter.”
Abu Dharr (r) once asked the Prophet Muhammad (s): “O Messenger of Allah, what is gheebah?” He replied: “It is to mention about your brother that which he detests.”
Abu Dharr (r) said: “O Messenger of Allah, what if that which is mentioned of him should actually be in him?” He (s) replied: “Know that when you mention that which is in him, you have committed his gheebah, and when you mention that which is not in him, then you have slandered him.”
Consequences of Backbiting The Prophet (s) once gave counsel to Abu Dharr (r) , saying: “O Abu Dharr! Beware of backbiting, for backbiting is graver than adultery (zina’).” Abu Dharr (r) said: “Why is that so, O Messenger of Allah?” He (s) replied: “That is because when a man commits adultery and then repents to God, God accepts his repentance. However, backbiting is not forgiven until forgiven by its victim.”
The Noble Messenger (s) said: “Whoever backbites a Muslim spoils his fasts and breaks his wudu', and shall come on the Day of Resurrection with his mouth's stench more putrid than a carcass', and it shall irk those who are with him in his station (mawqif). If he dies before repenting, his death is like that of one who dies while considering permissible that which is prohibited by God, the Exalted and the Glorious.”
Imam al-Sadiq (‘a) narrated from the Prophet (s) who said: “O you who have embraced Islam with your tongues but in whose hearts faith has not yet entered, do not disparage Muslims and do not seek their defects. Verily, God will seek out the defects of he who is after their defects; and one who has God after his defects will be humiliated, even in his own abode.”
Al-Kulayni, al-Kafi, vol. 2, "Kitab al-Iman wa al-Kufr", "Bab man talaba 'atharat al-Mu'minin", hadith no. 2
Imam al-Sadiq (‘a) narrated from the Prophet (s) who said: “The havoc wrought on the believer's faith by backbiting is swifter than the one wrought by aklah (a disease that consumes the flesh) in the side of his body.”
Al-Kulayni, al-Kafi, vol. 2, "Kitab al-Iman wa al-Kufr", "Bab al-Gheebah wa al-Buht", hadith no. 1
When backbiting ingresses into our conduct, it leaves adverse effects on the soul. One of these is cultivation of enmity and hatred towards the victim, which gradually increases. At the time of death, when the veils of the angelic realm (al-malakut)are lifted, the backbiter may be brought to witness the high station of his victims before God, and the honour and blessings bestowed on them by the Almighty Lord. The backbiter's hatred and enmity towards the person may then lead him to hate God Almighty! Thus, he will leave this world with enmity of God in his heart, and enter everlasting wretchedness.
Prohibition of Listening to Backbiting In the same manner as backbiting is prohibited, so also is listening to it. Indeed, as some traditions indicate, the listener is like the backbiter in all the evil aspects—so much so that his act is a grave sin carrying an obligation to seek forgiveness from the victim.
The Prophet (s) said: “The listener is one of the two backbiters.”
Al-Fayd al-Kashani, Al-Mahajjat al-Bayda', vol. 5, p. 260
Imam al-Sadiq (‘a) narrated from the Noble Messenger (s) who is once said to have forbidden both backbiting and listening to it. Then he (s) said: “Lo, whoever does a favour to his brother by refuting his backbiting upon hearing it in a gathering, God shall save him from a thousand kinds of evils in this world and in the Hereafter. And if he does not do so despite his ability to refute it, on him shall be the burden of one who commits his backbiting seventy times.”
Among the more subtle forms of backbiting is listening to it with amazement. Such a person expresses his amazement in order to make the backbiter more lively in his descriptions. His amazement encourages the latter in his evil act. For instance, he will say, “Strange” or “Astaghfirullah!”. Or he might say, “I didn't know that!” or “I didn't know he would do such a thing!” These expressions are meant to affirm the backbiter's statements and to encourage him to add something more. These acts are in fact the Devil's artifices. Surely, to affirm backbiting is also backbiting; as is to listen to it, or even to remain silent upon hearing it.
al-Shahid al-Thani's Discourse as quoted in Forty Hadith by Ayatullah Khumayni.
Is Backbiting Ever Allowed? There are very few situations where it is permissible to speak about the faults of another person. One must be very careful not to let the existence of these exceptions allow transgression into sin. Some of these situations are:
to protect Muslims from the evil of another person, including situations where one is asked to vouch for the integrity of a marriage prospect
when the person being talked about does not conceal his violations of Divine commands
to describe any fault of a patient before a physician for purposes of treatment
criticism about a narrator of traditions (hadith).