Backbiting – mere words – but they are words that bring upon the one who utters them shame and ignominy and that consign him to the Fire. Such a person has given in to his vain desires and succumbed to his destructive tendencies.

The Prophet (peace be upon him) said: “A man might speak a word without thinking about its implications, but because of it, he will plunge into the Hellfire further than the distance between the east and west. [ Sahih al-Bukhari (6477) and Sahih Muslim (2988)]

A Muslim utters a word whereby he describes his brother Muslim in a negative way – either explicitly or implicitly – and it plunges the speaker into clear and evident loss. And what could be a greater loss than for a person to say something that does nothing for him but rob him of his blessings and of the rewards for his good deeds? Then, if his good deeds run out, the sins of the one he has backbitten are taken from that person and foisted upon the speaker until he is hurled by them into Hell.

A Muslim utters a mere word upon his tongue thoughtlessly, without any consideration, and without thinking that he will be taken to task for it. Indeed, it is something about which many people are heedless.

Once Mu’adh b. Jabal, the illustrious Companion, asked the Prophet (peace be upon him) to inform him of some good work that would admit him into Paradise and distance him from the Hellfire. The Prophet (peace be upon him) mentioned to him the virtues of many good deeds, then said: “Shall I inform you of the foundation of all of that?”
Mu’adh said: “Certainly.”
The Prophet (peace be upon him) took hold of his own tongue and said: “Restrain yourself from this.

Mu’adh then asked: “O Prophet of Allah! Are we held to task for the things that we say?”

The Prophet (peace be upon him) replied: “May your mother be bereaved of you, O Mu’adh! Does anything topple people headlong into the Hellfire save the harvests of their tongues?[Sunan al-Tirmidhi (2616) and Sunan Ibn Majah (3973)]

The Prophet (peace be upon him) said: “Whoever can guarantee to me what is between his two lips and what is between his two legs, I can guarantee for him Paradise. [Sahîh al-Bukhârî (6474)]

The Prophet (peace be upon him), when he said “what is between his two lips” was alluding to the words that a person speaks. To guarantee it means to only speak what Allah is pleased with. When he said ” and what is between his legs” he was alluding to sexual relations, meaning that the person guarantees that he will not engage in any unlawful sexual activity that is prohibited by Allah.

Backbiting can be defined as the utterance of words whereby one mentions his fellow Muslim in a bad way or mentions him in a manner that he would be displeased with. It is called backbiting because a person generally berates another person in that person’s absence.

The Prophet (peace be upon him) defines backbiting in the following way, and his definition is preferred over any other:

He said: “Do you know what backbiting is?

They said: “Allah and His Messenger know best.”

He said: “It is to mention about your brother something that he would dislike having mentioned about him.[Sahih Muslim (2589)]