The law of diyyat

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. And whoso finds this (the penance of freeing a slave) beyond his means, he must fast for two consecutive months in order to seek repentance from Allâh. And Allâh is Ever All¬Knowing, All¬Wise.

And whoever kills a believer intentionally, his recompense is Hell to abide therein, and the Wrath and the Curse of Allâh are upon him, and a great punishment is prepared for him.

An-Nisa 92