BUHTAN OR SLANDER
Buhtan or Slander, and the making of false accusations, are considered to be major sins in Islam. This involves fabricating or spreading a lie about your brother/ sister (Muslim) in his absence. 
بُهْتَان ( اسم ) : اِفْتِراء
- act of aspersing; damaging or derogatory remark
- slander or the act of slandering
- the invention of lies
- the act of lying ; a lie or lies
- the act of lying
- a lie or lies
- the noun gerund of verb to flaunt
- a trifle ; nonsense ;idle talk
- published false statement damaging to a person's reputation; defamatory written statement; act of publishing this
- intentially false statement; imposture
- vilification; defamation .
- defamation; slander; falsehood; calumniation
- the state of being false, esp. untrue
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.
Backbiting and slandering are shame and disgrace. Their perpetrator is detested and he shall not have a noble death.
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" Surah Al Hujurat 49: 12 
The Messenger (ﷺ) said: "Do you know what is gheebah (Backbiting)? They said: "Allah and His Messenger (peace be upon him) know best. He (peace be upon him) said, "Mentioning about your brother what he would hate (in his absence)'. It was said: 'What about if what I say about my brother is true?' He (peace be upon him) said: "If in him is what you say you would have backbited him, and if it is not in him. then he is slandered (Buhtaan)." Sahih Muslim 2589
Of course, slander is a more heinous sin than backbiting, since it involves not only backbiting but also lying with intent to maliciously dishonor a Muslim.
The Messenger ﷺof Allah also said: "...And whoever knowingly argues uselessly, Allah will continue to be angry with Him until he refrains from it, and whoever says about a believer, that which is not in him Allah will house him in a mill of the people of the fire of Jahannam until he leaves off what he said ..." Abu Dawood, Al-Haakim & others
Islam is a religion of peace, love and compassion. Lies, suspicion, backbiting, slander and gossip are totally alien to Islam. In fact, they are considered amongst the most destructive of major sins. This is so because these sins sow enmity and discord among the Muslim Ummah (nation) and lead to its destruction. They cause hostilities between people of the same household, and between neighbours, friends and relatives.
Islam demands that our relationship with mankind be one of sincerity and responsibility. It should be one where we have respect for the honour, reputation and privacy of others. Islam teaches us that we are not only held accountable for our attitudes and actions, but also for anything over which we have control or influence in our society or the world around us.
Many of us backbite and gossip without thinking. We think it is a minor matter, however, Allah reminds us to be careful, for even though we think we are doing something small, it is in fact very large in the sight of Allah!
Allaah Teaches Us to Speak Out Against Slander and Try to Put a Stop to It
Allaah Says (what means): "And why, when you heard it, did you not say: 'It is not for us to speak of this. Exalted are You, [O Allah]; this is a great slander?'" Surah Noor 24:16
Many people are so busy spreading the slander they hear that they do not even stop to consider whether it is true or not.
Satan Wishes that We Use Our Tongues to Create Conflict and Hatred. Allaah Says (what means): "And tell My servants to say that which is best. Indeed, Satan induces [dissension] among them. Indeed, Satan is ever, to mankind, a clear enemy."
Surah Isra 17:53
We Should Guard Our Tongue from Sins and Use Our Limbs in Acts of Obedience. Prophet Muhammad ﷺsaid: "He who protects his tongue from unlawful utterances and his private parts from illegal sexual intercourse, I shall guarantee him entrance into Paradise." Sahih Al-Bukhari & Sahih Muslim
The slander for which the hadd punishment must be carried out on the slanderer is accusation of zina (fornication or adultery) or homosexuality. In that case the slanderer must be given eighty lashes, if he does not produce four witnesses to testify to the truth of what he is saying, because Allaah says (interpretation of the meaning): “And those who accuse chaste women, and produce not four witnesses, flog them with eighty stripes” Surah al-Noor 24:4.
Words which may be used in slanderous ways are of two types: explicit or implicit. Explicit words are those which cannot be understood in any other way than as an accusation of zina or homosexuality, and the slanderer’s claims that he meant something other than slander cannot be accepted.
Examples include saying “O adulterer”, “You committed zina” or “O homosexual”.
It cannot be accepted if he says, “When I said ‘ya looti (O homosexual),’ I meant that he was a follower of the religion of Loot (peace be upon him), or that he did any of the actions of his people except that immoral action,” because this phrase, ‘ya looti’, cannot be understand in any way except as a accusation of immorality.
As for implicit phrases, these are words that may be taken as slander or they may be understood otherwise.
In this case the slanderer is to asked what he meant, and he has to tell the truth, because carrying out the hadd punishment on him in this world is easier to bear than punishment in the Hereafter. If he says: “I intended to slander him”, then he has slandered him, and if he says, “I meant something other than slander”, then there is no hadd punishment, but he should be given a disciplinary punishment for reviling people.
Examples of that include saying “O evildoer” and the like. 
In these days it has become very common that people who claim to have knowledge and to be calling people to good slander many of their brothers among the well-known daa’iyahs, and they talk about the seekers of knowledge, daa’iyahs and lecturers. They do that in secret in their own gatherings, but it may be recorded on tapes that are distributed among the people, and they may do it openly in public lectures in the mosques. This behaviour goes against the commands of Allaah and His Messenger in several ways.
1. It is a transgression against the rights of the Muslims, and against the elite of the people, namely the seekers of knowledge and daa’iyahs who are striving to make the people aware and to teach them and correct their beliefs and practices, and to organize lessons and lectures, and to write beneficial books.
2. It splits the Muslims and causes division in their ranks. They are the most in need of unity and they need to keep away from division, discord and too much gossip amongst themselves, especially when the daa’iyahs who are being slandered are from among the Ahl al-Sunnah wa’l-Jamaa’ah who are well known for their opposition to bid’ah (innovation) and myth, and for standing up against those who promote such things, and for exposing their plots and tricks. We see no benefit to be gained by such actions, except for the enemies who lie in wait for opportunities to harm the Muslims, such as the kaafirs, hypocrites and followers of bid’ah and misguidance.
3. This action offers support and help for the self-serving among the secularists, westernizers and other heretics who are well known for stirring up trouble among the daa’iyahs and telling lies against them, and inciting people against them in their writings and recordings. It is contrary to Islamic brotherhood for those who are too hasty to help their enemies against their brothers among the seekers of knowledge, daa’iyahs and others.
4. This spreads corrupts ideas in the hearts and minds of the common folk and elite; it spreads and propagates lies and false rumours, and causes a great deal of backbiting and slander. It leaves the door wide open to evil people who persist in spreading doubts and stirring up fitnah, and who are keen to cause harm to the believers by accusing them of things that they did not do.
5. Much of what is being said has no basis in reality; rather these are illusions which the Shaytaan has made attractive to them, through which he has tempted them.
6. Whatever ijtihaad is produced by some scholars or seekers of knowledge, in areas where ijtihaad is permitted, the author of said ijtihaad cannot be blamed or rebuked for it, so long as he is qualified to engage in ijtihaad. If someone else has a different opinion, it is better for him to debate with him in a proper manner, striving to reach the truth via the shortest route and leaving no room for the insinuating whispers of the Shaytaan or for him to cause trouble among the believers. If that is not possible, and someone thinks that he has no choice but to explain what is wrong with his ijtihaad, then he should choose the best wording and the most subtle way of explaining, and not resort to attacking, slandering or going to extremes in criticizing him, which may cause others to reject the truth or to turn away from it. He should also avoid criticizing specific people, casting aspersions upon their intentions or saying unnecessary or irrelevant things about them. In such cases the Messenger ﷺwould say, “What is the matter with some people who say such and such…?”