Violation on others' life and depriving an individual of his right to live, in the eyes of Islam is the biggest sin. The Prophet of Islam (PBUH) said: "Seeing the destruction of the world is easier for God than seeing a believer being murdered."1
Islam promises a killer to stay in hell perpetually:
وَمَنْ يَقْتُلْ مُؤْمِنًا مُتَعَمِّدًا فَجَزَاؤُهُ جَهَنَّمُ خَالِدًا فِيهَا وَغَضِبَ اللَّهُ عَلَيْهِ وَلَعَنَهُ وَأَعَدَّ لَهُ عَذَابًا عَظِيمًا
But whoever kills a believer intentionally - his recompense is Hell, wherein he will abide eternally, and Allah has become angry with him and has cursed him and has prepared for him a great punishment. (Quran, 4:93)
Furthermore, in the Islamic law, the punishment for killing someone without a legal permit in this world is execution. The Holy Quran says:
وَلَا تَقْتُلُوا النَّفْسَ الَّتِي حَرَّمَ اللَّهُ إِلَّا بِالْحَقِّ ۗ وَمَنْ قُتِلَ مَظْلُومًا فَقَدْ جَعَلْنَا لِوَلِيِّهِ سُلْطَانًا فَلَا يُسْرِفْ فِي الْقَتْلِ ۖ إِنَّهُ كَانَ مَنْصُورًا
And do not kill the soul which Allah has forbidden, except by right. And whoever is killed unjustly - We have given his heir authority, but let him not exceed limits in [the matter of] taking life. Indeed, he has been supported [by the law]. (Quran, 17:33)
One of the outstanding characteristics of the Islamic law was a serious fight against the inhuman act and tradition of burying their infant daughters alive. Before the advent of Islam, the girls used to be buried alive. But at the advent of Islam it was immediately banned. As Islam being strictly against it, protested and firmly fought against this savage vicious crime.
The Holy Quran says: ‘Those who buried these girls alive will be interrogated on the Resurrection Day. They will be asked: Which sin had they committed to deserve death?”2
Another vital point is that the Islamic law attaches great significance not only to the adults' lives but also to children's right to life.
This verse of the Holy Quran is indicative of the significance of this reality:
وَلَا تَقْتُلُوا أَوْلَادَكُمْ خَشْيَةَ إِمْلَاقٍ ۖ نَحْنُ نَرْزُقُهُمْ وَإِيَّاكُمْ ۚ إِنَّ قَتْلَهُمْ كَانَ خِطْئًا كَبِيرًا
… And do not kill your children for fear of poverty. We provide for them and for you. Indeed, their killing is ever a great sin. (Quran, 17:31)
Another issue is that if there are some accomplices who conspire and commit a murder together, this does not alleviate or lessen the burden of the crime or the sin of the killers. The Prophet of Islam (S) said: "Cooperation in killing no matter to what extent will cause disappointment and distance from God's mercy on the Resurrection Day."3
Once, during the Prophet's time, a man was killed in the city of Medina by a group of people. No certain individual was identified as the killer. So as soon as the Prophet (S) heard the news, he rushed to the mosque to speak and announced:
"If all the residents of Heaven and Earth participate in killing a human, they will all suffer punishment.”4
Also forbidding murder and depriving a person of life, is not exclusively allocated to Muslims, but anyone living under the umbrella of an Islamic government enjoys this right, but as long as they do not intend to overthrow the Islamic state to fight against it. Thus, their blood, property and lives will benefit from this sanctity and thus, will benefit from the Islamic state's protection. Thus, the Prophet (S) said: "God will forbid (going to) the Heaven for he who kills a sinner."5
The Islamic ruling against murder is so strict that even if someone gives shelter to a murderer, he will face strict and severe blame. The Prophet (S) said: "He who gives shelter to a killer or someone who causes or paves the way for a murder, he will be condemned by God.”6
This point is also remarkably important in regards to depriving others of their lives: in the Islamic law reluctance or compulsion does not justify the act of murder. Therefore if someone is threatened to be killed should he refuses to commit a murder, his crime is not justifiable. The threatened person has no right to kill another person, just to rescue himself from death, as the value of all men is the same and has sanctity. But the opposite is better, as the Prophet (S) was quoted as saying: "If you are in a situation where you can prevent a believer, who says his prayer, from being killed by you (otherwise you would lose your life), you must prefer to be killed than commit this crime."7
As repeatedly seen in the history of the holy wars at the advent of Islam, some self-sacrificing men during the war sacrificed their own lives by giving their very last date to their comrades in the warfront who were starving to death to rescue them. Thus they were honored to be martyrs.