It is not for a believer to kill a believer except ( that it be ) by mistake , and whosoever kills a believer by mistake , ( it is ordained that ) he must set free a believing slave and a compensation ( blood money , i.e. Diya ) be given to the deceased 's family , unless they remit it . If the deceased belonged to a people at war with you and he was a believer ; the freeing of a believing slave ( is prescribed ) , and if he belonged to a people with whom you have a treaty of mutual alliance , compensation ( blood money - Diya ) must be paid to his family , and a believing slave must be freed .