مَنْ قَتَلَ نَفْسًا بِغَيْرِ نَفْسٍ أَوْ فَسَادٍ فِي الْأَرْضِ فَكَأَنَّمَا قَتَلَ النَّاسَ جَمِيعًا
Whoever kills a person, other than in the cases described of another life or corruption in the land, is as though he killed all humanity. (Al-Ma'idah 5:32)
The sanctity of life is expressed in exceptionally strong terms. Unlawful killing wrongs the victim and gravely violates the security of human life. Decisions affecting life therefore cannot be grounded in speculation or used to justify personal revenge.