Bukhari

Chapter. The Statement of Allah: “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 believers; 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 must be paid to his family, and a believing slave must be freed. And whose finds this (the penance of freeing a slave) beyond his means, he must observe fast for two consecutive months in order to seek repentance from Allah. And Allah is ever All-Knowing, All-Wise.” (V.4:92)