Major sins are indeed the cause for all misery, evil and torment in this world and the hereafter.
And the worst of all sins are those that are greatest in harm and danger to humanity. Among the destructive major sins are backbiting and slandering. These two sins are forbidden by Allah because they sow enmity, evils and discord among people and lead to destruction. They cause hostilities between people of the same household and between neighbors and relatives. They can decrease in good deeds and increase in evil ones and lead to dishonor and ignominy.
Continue after the cut...
Backbiting and slandering are shame and disgrace. Their perpetrator is detested and he shall not have a noble death. Allah forbids these acts, as He says in the Qur'an:
"Backbiting and Gossiping are from the most vilest and despicable of things, yet the most widely spread amongst mankind, such that no one is free from it except for a few people."
Backbiting (gheebah) means mentioning something about a person (in his absence), that he hates (to have mentioned), whether it is about: His body, his religious characteristics, his worldly affairs, his self, his physical appearance, his character, his wealth, his child, his father, his wife, his manner of walking, his smile, it is the same whether you mention that about him with words, through writings, or whether you point or indicate him by gesturing with your eyes, hand or head.
As for the body, is when you make fun of how someone looks, or mentioning any bad quality in him, as saying: "he is blind", "he limps", "he is bleary-eyed", "he is bald", "he is short", "he is tall", "he is black", "he is yellow", "he's too thin", "he's too fat". As for his religious qualities, it is when you say: "he is a sinner", "he is a thief", "he is a betrayer", "he is an oppressor", "he doesn't pray", "he prays so fast", "he does not behave well towards his parents", "he does not pay the Zakat duly"." As for the worldly matters, then it is when you say: "he has poor manners", "he does not think that anyone has a right over him", "he talks too much" …etc
Allah says in the Qur'an:
"O you who believe! Avoid much suspicion, in deeds some suspicions are sins. And spy not 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 Allah, verily, Allah is The One Who accepts repentance, Most Merciful" (Qur'an 49: 12)
In this verse, Allah strongly forbids backbiting, and he compares the backbiter to one who eats the flesh of his dead brother. If he would hate eating the flesh of his brother, he should also hate to eat his flesh while he is alive by backbiting and slandering him.
When one reflects deeply over this assimilation it will be enough to keep one away from backbiting.
Abu Hurayrah (May Allah be pleased with him) narrated that Prophet Mohammad (PBUH) said:
"Do you know what backbiting is?” They said, “Allah and His Messenger know best.” He then said, “It is to say something about your brother that he would dislike.” Someone asked him, “But what if what I say is true?” The Messenger of Allah said, “If what you say about him is true, you are backbiting him, but if it is not true then you have slandered him."
Backbiting is so widespread among people that it has become an issue of people’s meetings and an avenue for expressing their anger, misgivings and jealousy. Those who indulge in backbiting are hiding their own imperfections and harming others. They are oblivious of the fact that they are only harming themselves.
This is because the backbiter if the wrongdoer and his victim is the wronged, on the Day of Resurrection both the wrongdoer and the wronged will stand before Allah Who is the Just Judge and the wronged will appeal to Allah to avenge the wrong done to him, Allah will then give this wronged person from the good deeds of the person who wronged him in accordance with his wrong by backbiting his brother on a Day that no father will give his son any of his good deeds nor a friend to his friend. All will be saying, ‘Myself, myself.’
Ibn 'Abbas (May Allah be pleased with him) reported that Prophet Mohammad (PBUH) once passed by two graves and said:
"Verily, they (occupants of graves) are both being tormented and they are not being tormented for something major." In the report from Al-Bukhari:
"Rather, it is indeed something major. As for the first one, he used to go around spreading gossip (nameemah) and as for the other, and then he used not to protect himself from his own urine." 
The scholars say the meaning of "and they are not being tormented for something major" is "something major" according to their opinion or "something major" for them to have abandoned doing.
Prophet Mohammad (PBUH) also said:
"Who protects his tongue from unlawful utterances and his private parts from illegal sexual intercourse; I shall guarantee him entrance into Paradise."
Also Abu Mousa Al-Ash’aree narrated that Prophet Mohammad (PBUH) said:
"I asked the Messenger of Allah: Who is the best Muslim? The Messenger of Allah replied, "He is the one from whom Muslims are safe from the evil of his tongue and hands."
And Abu Sa’eed Al-Khudree narrated that Prophet Mohammad (PBUH) said:
"When man wakes up in the morning each day, all parts of the body warn the tongue saying, ‘Fear Allah as regards us for we are at your mercy; if you are upright, we will be upright and if you are crooked, we become crooked."
So, Muslims, you should beware of slipping of your tongues and do not give it free hand to wreak havoc on you. For a too free tongue destroys its owner and causes him calamities and evils.