Quran 4:92

Never should a believer kill another believer, except by mistake. If anyone kills a believer by mistake he must free one Muslim slave and pay compensation to the victim’s relatives, unless they charitably forgo it; if the victim belonged to a people at war with you but is a believer, then the compensation is only to free a believing slave; if he belonged to a people with whom you have a treaty, then compensation should be handed over to his relatives, and a believing slave set free. Anyone who lacks the means to do this must fast for two consecutive months by way of repentance to God: God is all knowing, all wise