Аль-Бакара 2:179

Islam has laid down the principle of retaliation in like measure (qisas). For example, ‘an eye for an eye and a tooth for a tooth’. Retribution for a killer means the forfeiture of his own life. In this way, on the one hand, a capital crime like the taking of life is effectively discouraged, for the fear of losing one’s own life deters one from taking another’s life and, as a result, the life of all the members of a society become protected. The killing of the killer guarantees the saving of lives in a society. Thus the objective of qisas is the protection of the members of society, and not revenge. Moreover, the vengeful feelings of the family of the murdered person are cooled, thus obviating the possibility of any further injurious activity. However, qisas in Islam permits a settlement to be arrived at between the killer and the killed. The heirs of the deceased person may, of course, opt for the execution of the killer, but they may also, if they so wish, accept blood-money instead, or even forgive him. The main aim of these alternatives is to guarantee the prevalence of brotherly feeling in Islamic society, and to prevent an atmosphere of rivalry taking root. Then the principle of blood-money has the special advantage of giving the bereaved family monetary compensation for the death of one of its members.