Allah, the Almighty, says,
If a man kills a believer intentionally, his recompense is Hell, to abide therein (forever); and the wrath and curse of Allah are upon him, and a dreadful chastisement is prepared for him.
Those who invoke not, with Allah, any other god, nor slay such life as Allah has made sacred, except for just cause, nor commit fornication,' and any that does this (not only) meets punishment.
On that account: We ordained for the children of Israel that if anyone slew a person -unless it be for murder 'or for spreading mischief in the land -it would be as if he slew the whole people.
When the female (infant), buried alive, is questioned - for what crime she killed.
The Prophet (pbuh) said,
"Avoid the seven heinous sins."
(Al- Takwir: 8-9)
And he mentioned taking one's life which Allah has made sacred except in the course of justice.
It was related that someone asked the Prophet (pbuh),
"What is the most heinous sin in the sight of Allah?" The Prophet replied, "To hold that Allah has an equal whereas He has created you." .The man asked, "What else?" The Prophet said, "To kill your child lest he feeds with you." The man asked, "What else?" He said, "To commit adultery with your neighbor's wife.”
Therefore, Allah, the Almighty, revealed,
Those who invoke not, with Allah, any other god, nor slay such life as Allah has made sacred, except for just cause, nor commit fornication,. and any that does this (not only) meets punishment.
It was related that the Messenger of Allah said,
"When two Muslims meet with drawn sword, both the slayer and the slain are in the Hell." It was said, "0 Messenger of Allah, that is for the slayer. But why the slain?" He replied, "Because his intention was to kill the other.”
Abu Suliman Al-Khitabi commented, "Such punishment does not apply to a legal and justifiable combat. They entail this abode if they fight one another out of enmity, fanaticism, to acquire some worldly benefit or a position of leadership. Thus, out of this pole is the one who fights against an aggressive Muslim if he follows the rules of fighting and the one who defends himself without intending to kill the opponent.
Whoever fights against an aggressive Muslim or a highway robber, should not seek to kill them. Rather he should try to deter him as much as he can. When they refrain we should refrain. The Prophet (pbuh) said,
"You should not turn an unbeliever when I am no more (among you) and start killing and shedding blood among yourselves.”
The Prophet (pbuh) said,
"The first thing among human beings to be adjudicated on the Day of Judgment, will be the blood claim.”
"Taking a believer's life is more grievous in Allah's sight than the perishing of this world.”
"The major sins are worshipping others with Allah, showing disrespect to parents, killing a human being, and the breaking one's oath.”
It is termed engulfing because it overwhelms its swearer in the Fire.
"For all the murders committed in this world without any justification, prophet Adam's son, Qabil will get a share of punishment, because it was he who inaugurated the method of killing by murdering his brother Habil.”
"Whoever killed anyone of the people of the covenant will never get the aroma of paradise which can be smelt from forty years away.”
"Whoever helps in killing a Muslim even by just a part of a word, he will meet Allah with the written phrase on his forehead "Despondent of Allah's Mercy.”
"Every sin might be forgiven by Allah except for a man dying an unbeliever or a man killing a believer deliberately.”
Ascribing Associates To Allah, the Most High (Shirk)
Killing A Human Being
Not Performing The Prayer
Not Paying Zakat
Breaking One's Fast During Ramadan Without An Excuse
Not Performing the Hajj when Able to
Showing Disrespect to One's Parents
Severing the Ties of One's Relatives
Accepting Usurious Gain
Wrong Consuming An Orphan's Property
Lying About The Prophet
Fleeing From The Battlefield
The Leader Who Misleads His Followers, The Tyrant And The Oppressor
Arrogance, Pride, Conceit, Vanity And Haughtiness
Bearing False Witness
Accusing A Woman Of Adultery
Misappropriating Spoils Of War, Muslim Funds Or Zakat
Highwaymen Who Menace The Road
The Engulfing Oath
Taking People's Property Through Falsehood
The Consumption of Haram
The Dishonest Judge
Women Imitating Men And Vice Versa
The Pimp and the one Who Permits His Wife to Fornicate
Marrying Solely To Return To The Previous Husband
Not Freeing Oneself Of All Traces Of Urine
Showing Off In Good Work
Learning Sacred Knowledge For The Sake Of This World, Or Concealing It
Breach of Trust
Reminding Recipients of Ones Charity To Them
Disbelieving In Destiny (qadar)
Listening To People's Private Conversations
The Talebearer Who Stirs Up Enmity Between People
Breaking Promises or Pledges
Believing Fortune Tellers And Astrologers
Wife Rebelling Against Her Husband