In the name of Allah most Gracious most Merciful.

The major sins are those acts which have been forbidden by Allah in the Quran and by His Messenger (pbuh) in the Sunna (practice of the Prophet), and which have been made clear by the actions of the first righteous generation of Muslims, the Companions of the Prophet (pbuh).

Allah (swt) says in the Glorious Quran:

“If you avoid the major (part) of what you have been forbidden (to do), We will cancel out for you your (other) evil deeds and will admit you (to Paradise) with a noble entry.” (Al Nisa;31)

It is therefore very important to determine exactly what the greatest vices, technically called “the major sins” are, in order that Muslims avoid them. The prophet (pbuh) said: “Avoid the seven noxious things” – and after having said this, the Prophet (pbuh) mentioned them: “Associating anything with Allah; magic, killing one whom Allah has declared inviolate without a just cause, consuming the property of an orphan, devouring usury, turning back when the army advances, and slandering chaste women who are believers but indiscreet.” (Bukhari and Muslim)

The greatest of all major sins is Shirk – that is to say, associating anyone with Allah Most High, and it is of two kinds. The first is to believe that Allah has an equal or to worship something or someone other than Him. This is the greatest Shirk, about which Allah Most High says:

“Indeed Allah does not forgive associating anything with Him, and He forgives whatever is other than that to whomever He wills.” (Al Nisa: 48)

The second kind of associating anything with Allah is insincerity and ostentation of one’s deeds, as stated by Allah Most High:

“Anyone who is expecting to meet his Lord should act righteously and not make anything as a sharer in the worship of his Lord.” (Al Kahf; 110)

That is to say, in all one’s deeds, one ought not act for the sake of ostentation but sincerely, for the sake of Allah alone.

Allah’s Messenger (saw) said: “If anyone does anything in which he associates another with Me, his action belongs to the one for whose sake he did it and I am clear of it.” (Muslim and Ibn Majah)

Murder is the second major sin. Allah Most High says:

“And if anyone kills a believer deliberately, his recompense is Hell, to remain therein forever. And Allah’s anger will be upon him and His curse, and a great punishment will be prepared for him.” (Al-Nisa: 93)

Allah’s Messenger (saw) said: “A believer will continue to find ample scope in his religion as long as he does not kill anyone unlawfully.” (Bukhari, Muslim) and..

“Shedding of blood will be the first matter about which judgement will be given on the Day of Resurrection.” (Bukhari and Muslim)

The third major sin is practicing magic. Magicians are necessarily unbelievers. The prescribed punishment for a magician is death, since magic constitutes unbelief in Allah and is a source of spreading unbelief among people. Allah Most High says:

“But the evil ones (shayateen) disbelieved, teaching the people magic…. (Al-Baqarah: 102)”

Allah’s Messenger (saw) said: “Avoid the seven noxious things,” and among them he mentioned magic. Of course, noxious things are fatal, and a person should fear his Lord and not dabble in things which will bring him loss in this world and in the next.

The fourth major sin is to consume interest. Allah Most High says:

“O you who believe, do not consume interest, doubled and multiplied. And be conscious of Allah in order that you may be successful.” (Ale-Imran: 130) “Those who consume interest will not stand except as one stands whom Satan has destroyed by his touch. That is because they say: “Trade is like interest.” (Al-Baqarah: 275)

On the Day of Resurrection, people will rise from their graves quickly, excepting those who had consumed interest. They will stand up and then fall down like epileptics because they consumed interest in this world. Allah will fill their stomach with something heavy, due to which they will not be able to stand without falling down. They will try to hasten along with the other people but will not be able to do so.

Allah’s Messenger (saw) said: “During my Ascension, in the Seventh Heaven, I heard thunder and lightning over my head, and I saw people with their stomachs as large as houses between their hands; and inside their stomachs, snakes and scorpions were visible from the outside. I then asked, ‘Who are these, Gabriel?’ and he replied, “The consumers of interest.” (Ahmad)

The fifth major sin is to wrongfully consume the property of an orphan.

Allah Most High says: “Truly, those who wrongfully eat up the property of orphans, consume fire in their bellies, and they will roast in a blaze.” (an-Nisa:10)

Abu Hurairah (ra) reported Allah’s Messenger as saying: “Allah who is Great and Glorious will raise from their graves a group of people having fire in their bellies and fire coming out of their mouths.” The listeners asked him: “Who are they, Messenger of Allah?” He said: “Do you not know that Allah Most High says, “Truly, those who wrongfully eat up the property of orphans, consume fire in their bellies.”

The sixth major sin is to run away from the battlefield.

Allah Most High says: “O you who believe, when you meet in battle those who disbelieve, do not turn your backs on them. And whoever turns his back on them that day, unless maneuvering to battle or moving to join another company, has truly incurred the anger of Allah and his habitation will be Hell, and (how) evil a destination! (al-Anfal: 16)

Ibn Abbas (ra) said: “When the verse was revealed, ‘If there are twenty steadfast ones among you, they will overcome two hundred’ (al-Anfal: 65), Allah prescribed to the Muslims that if there were twenty of them against two hundred of the enemy, they must not run away (but must fight).

The seventh major sin is to slander chaste women. Allah has made it clear in the verses that anyone who falsely accuses chaste believing women of adultery (or fornication) and lewdness is cursed in this world and the Hereafter, and he will have a tremendous punishment. In this world, he will be punished with eighty lashes, and his testimony will never be accepted thereafter.

Allah Most High says: “Truly, those who cast blame upon chaste (but) indiscreet believing women are cursed in this world and the Hereafter. And there will be a tremendous punishment for them, on the Day when their tongues, their hands, and their feet will testify against them concerning what they used to do. (al-Nur: 23-24)

Allah’s Messenger (saw) said: The man who pronounces words (of accusation) without evidence will falter (on the bridge) and will fall into the Fire for a distance greater than that which is between the East and the West.

The other Major Sins are:

Not Praying,
Not paying Zakat,
Not fasting on a Day of Ramadan without excuse,
Not performing Hajj, while being able to do so,
Disrespect to parents,
Abandoning relatives,
Fornication and Adultery,
Homosexuality (sodomy),
Lying about Allah and His Messenger,
A leader’s deceiving his people and being unjust to them,
Pride and arrogance,
Bearing false witness,
Drinking Khamr (wine),
Stealing from the spoils of war,
Highway Robbery,
Taking false oath,
Illegal gain,
Consuming wealth acquired unlawfully,
Committing suicide,
Frequent lying,
Judging unjustly,
Giving and Accepting bribes,
Woman’s imitating man and man’s imitating woman,
Being cuckold,
Marrying a divorced woman in order to make her lawful for the first husband,
Not protecting oneself from urine,
Learning knowledge of this religion for the sake of this world and concealing that knowledge,
Betrayal of trust,
Recounting favours,
Denying Allah’s Decree,
Listening peoples’ private conversations,
Carrying tales,
Breaking contracts,
Believing fortune-tellers and astrologers,
A woman’s bad conduct toward her husband,
Making statues and pictures,
lamenting, wailing, tearing the clothing, and doing other things of this sort when an affliction befalls,
Treating others unjustly,
Overbearing conduct toward the wife, the servant, the weak, and animals,
Offending one’s neighbour,
Offending and abusing Muslims,
Offending people and having an arrogant attitude toward them,
Trailing one’s garment in pride,
Men’s wearing silk and gold,
A slave running away from his master,
Slaughtering an animal which has been dedicated to anyone other than Allah,
To knowingly ascribe one’s paternity to a father other than one’s own,
Arguing and disputing violently,
withholding excess water,
Giving short weight or measure, Offending Allah’s righteous friends,
Not praying in congregation but praying alone without an excuse,
Persistently missing Friday prayers without any excuse,
Usurping the rights of the heir through bequests,
Deceiving and plotting evil,
Spying for the enemy of Muslims,
Cursing or insulting the Prophet’s companions.

Ref: ‘Al-Kabaar’ by Muhammad Bin Uthman;
‘The Major Sins’ by Mohammad Moinuddin Siddiqui.