Depriving Oneself of Life is Forbidden (Sanctity of One's Life)
A remarkable point in the subject of "right to life" is Islamic law is banning suicide. The Holy Quran explicitly prohibits individuals from depriving themselves of life.
يَا أَيُّهَا الَّذِينَ آمَنُوا لَا تَأْكُلُوا أَمْوَالَكُمْ بَيْنَكُمْ بِالْبَاطِلِ إِلَّا أَنْ تَكُونَ تِجَارَةً عَنْ تَرَاضٍ مِنْكُمْ ۚ وَلَا تَقْتُلُوا أَنْفُسَكُمْ ۚ إِنَّ اللَّهَ كَانَ بِكُمْ رَحِيمًا
…. and do not kill yourselves [or one another]. Indeed, Allah is to you ever Merciful. (Quran, 4:29)
In the eyes of Islam a person's body, soul, and life belongs to God. He is the one who gives life and whenever he decides he can take it back. Since the goal of creation and giving life to mankind is his achieving perfection and felicity, therefore and in reality suicide means a retreat from achieving perfection and also a decline and downfall into the valley of failure and loss of mankind.
The Prophet (S) was quoted as saying: "Whoever commits suicide by means of some instrument, he will be tormented on the Resurrection Day by the same tool."1 Also according to another narration he has been quoted as saying: "If someone suffocates himself he has put himself in the hell fire and he who hits himself by a spear is in fire."2
You should know that sin of killing oneself is Islam is absolute, the same way that killing others is a sin, committing suicide is also a sin and unlawful. Depriving yourself of life is one of the major sins. The Holy Quran has promised severe punishment for the individual who terminates his own life:
وَمَنْ يَفْعَلْ ذَٰلِكَ عُدْوَانًا وَظُلْمًا فَسَوْفَ نُصْلِيهِ نَارًا ۚ وَكَانَ ذَٰلِكَ عَلَى اللَّهِ يَسِيرًا
And whoever does that in aggression and injustice - then we will drive him into a Fire. And that, for Allah, is [always] easy. (Quran, 4:30)
There are different motives for suicide including: Weak religious beliefs, weak spirituality and religious ethics, excessive tendency or eagerness toward material things including all worldly demands, Insanity (mental disorder), and intolerable physical illness.
None of the aforementioned factors or reasons is justifiable in the eyes of Islam for committing such a great sin. But any goodness or evil (vicious) a man faces during his lifespan stems from a good or an evil deed which is the reward or punishment of that deed. Or it could be a test by God. If Man faces such difficulties he must be patient and must tolerate them, and should choose reform and gratitude. The Holy Quran invites the believers to tolerate with assiduity, patience and endurance.
يَا أَيُّهَا الَّذِينَ آمَنُوا اسْتَعِينُوا بِالصَّبْرِ وَالصَّلَاةِ ۚ إِنَّ اللَّهَ مَعَ الصَّابِرِينَ
O you, who have believed, seek help through patience and prayer. Indeed, Allah is with the patient. (Quran, 2:153)
Thus, the divine religions, particularly Islam, severely oppose Euthanasia and consider it a way of suicide. Apparently, Euthanasia for a person suffering from an incurable illness is ignoring human dignity and mankind's supreme life value. Both non-voluntary (non-voluntary Euthanasia) and emergency death (desperate Euthanasia) are considered unlawful according to Islam law.
Thus not only the killed patient will suffer his punishment but also the person who according to his own demand (his diagnosis) actually commits such kind of killing will be punished as a murderer. Thus, it does not matter if the killed patient had announced his willingness or agreement before death.
As a patient's agreement does not help in any way in lessening the crime, there is no difference whether or not he has agreed. So one's act of Euthanasia is subject of unlawfulness of a murder.
The Prophet (S) was quoted as narrating the following story: "Once there was a man whose hand was wounded. The pain was so severe and intolerable that he cut his hand and then died of blood loss. Then God said he preceded me in taking his life. That is why I announce that he is deprived of heaven."