The Prophet God, Allah, says ( which means):”The slain person will come on the Day of Resurrection, holding his head in one hand and with the other hand he would be holding the killer by the chest; his (the slain person’s) veins would be bleeding until he reaches Al-‘Arsh (the Throne), then he would say: ‘This man has killed me’. Allah will then say to the killer: ‘Perish you!
He will then be taken to the Hellfire”. (a sound Hadith narrated by Termithi and Tabrani )
“A believer remains at liberty regarding his religion unless he kills somebody unlawfully.” (Related by Al-Bukhari)
Ibn ‘Umar (May Allah be pleased with them) commented on that Hadith saying: “One of the evil deeds with bad consequence from which there is no escape for the one who is involved in it is to kill someone unlawfully.”
“It is hoped that Allah may forgive every sin, except in the case of one who dies a polytheist, or the one who purposely kills a believer.”(Al-Targhib wa Al-Tarhib: 3/277)
It is a manifestation of the dignity of man that Islam has placed an infinite value on human life. This is expressed in the Qur’an in the following terms:
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 of mankind. And if anyone saved a life, it would be as if he saved the life of a whole people. (al-Ma’ida, 5:32)
The reference to the children of Israel, that is, the Jews, represents continuity of the basic values that are common to all revealed religions. Both Judaism and Islam are committed to the protection of human life. It makes no difference whether the victim is a Jew, a Muslim or anyone else. The value that is advocated is holistic and indivisible in that aggression against one is tantamount to aggression against all. Life is not only of infinite value, it is also sacred: “Nor take life which God has made sacred, except for a just cause” (al-Isra’, 17:33).
Al-Ghazali has quoted these ayat and drew the conclusion that “in respect of the sanctity of life and the prohibition of aggression against it, Muslims and non-Muslims are equal. Attack on the personal safety of non-Muslims invokes the same punishment in this world and the Hereafter”. [Muhammad Al-Ghazali, Huquq al-Insan, p. 54]
In times of military engagement, the warriors are under a personal duty not to destroy civilian life. It is consequently unlawful to attack women and children, the elderly and the insane, the ill and the invalid and this include the blind, the lame, the crippled and the unconscious. The exempted categories also include the priest and the monk and those engaged in worship as I well as farmers who occupy themselves with their works in the field provided that they are not involved in the conflict. The hadith contains detailed instructions on all of these and the Prophet has generally advised military commanders and soldiers in the battlefield to be fair, avoid excessive violence and incline toward peace. [Zuhaili has quoted five hadiths on the subject. See for details, Zuhaili, al-Fiqh al-Islami wa Adillatuh, VI, 421 ff.]
Plus Sanctity of the believer
The Prophet (peace be upon him) said:” Avoid the seven noxious things. It was said (by the hearers): What are they, Messenger of Allah? He (the Prophet) replied: Associating anything with Allah, magic, killing of one whom God has declared inviolate without a just cause…” (Related by Al-Bukhari and Muslim). “The first (thing) that will be decided among people on the Day of Judgment will pertain to bloodshed.” (Related by Al-Bukhari and Muslim)
“If a man kills a believer unjustly, Allah will not accept any action or duty of his, obligatory or supererogatory”
“If the dwellers of heaven and the inhabitants of earth collaborated in killing a believer, Allah would cast them all down into the hellfire.” (Reported by Al-Tirmidhi: 1398)
The Prophet (peace be upon him) said while making Tawaf (circumambulation) round the Ka‘bah, “How excellent you are! How beautiful your fragrance is! How great and sanctified you are! By Him in Whose Hand is the life of Muhammad, the sanctity of the believer’s life and property is greater in the sight of Allah than you; no one should think about him except good.” (Al-Targhib wa Al-Tarhib: 3/276)
“The vanishing of the entire world is less in value in the sight of Allah than killing a Muslim.” (Reported by Al-Tirmidhi: 1395)
Based on the above proofs (from the Qur’an and Sunnah) we can conclude the following:
First: It is forbidden to kill Muslims without a rightful claim as it is regarded one of the gravest sins.
Second: The Prophet (peace be upon him) made it equal to associating partners with Allah in worship; a sin which Allah does not forgive.
Third: Whoever kills a Muslim purposely will face the wrath, curse, severe torture and eternity in the Hellfire.
Fourth: The forbidden killing is the first grievance to be judged between the servants on the Day of Resurrection and the disgrace will be the share of the one who killed a Muslim without a rightful claim.
Fifth: Killing Muslims without a rightful claim is a predicament from which extrication is not possible.
Sixth: The sanctity of the lives of Muslims is greater than the sanctity of the Ka‘bah. The annihilation of the entire world is less significant in the sight of Allah when compared to killing a Muslim.
Seventh: Being instrumental in killing a Muslim by any means counts as involvement in the crime and leads to receiving the same punishment of casting in the hellfire, even if the doers were all the dwellers of the heaven and the inhabitants of earth; this indicates the great sanctity of the Muslim’s life.
Eighth: Whoever kills a Muslim unjustly, his good deeds will not be accepted at all.
Ninth: Killing Muslims pleases Iblis, the accursed enemy of Allah.
All the above discusses killing a Muslim without a rightful claim; what if we add to that the bombing of properties, terrifying the secured Muslims, committing suicide, as well as other grave sins which cannot be perpetrated except by those whose hearts were sealed and misdeeds have been made attractive so they consider them good. Allah, the Exalted, said:
“Say (O Muhammad peace be upon him): ‘Shall We tell you the greatest losers in respect of (their) deeds? Those whose efforts have been wasted in this life while they thought that they were acquiring good by their deeds! They are those who deny the Ayât (proofs, evidences, verses, lessons, signs, revelations, etc.) of their Lord and the Meeting with Him (in the Hereafter). So their works are in vain, and on the Day of Resurrection, We shall assign no weight for them.'”(Surat Al-Anbia’, 21:70-72)
“And of mankind there is he whose speech may please you (O Muhammad peace be upon him), in this worldly life, and he calls Allah to witness as to that which is in his heart, yet he is the most quarrelsome of the opponents. And when he turns away (from you “O Muhammad peace be upon him”), his effort in the land is to make mischief therein and to destroy the crops and the cattle, and Allah likes not mischief. And when it is said to him, “Fear Allah”, he is led by arrogance to (more) crime. So enough for him is Hell, and worst indeed is that place to rest!” (Surat Al-Baqarah, 2:204)