The Noble Qur'an Encyclopedia

It is not for a believer to kill another believer except by mistake. Whoever kills a believer by mistake[67] must free a believing slave and pay blood money to his family, unless they waive it as an act of charity. But if the victim was a believer and belonged to people at war with you, then a believing slave must be freed. If he belonged to a people with whom you have a treaty, then blood money must be paid to his family and the freeing of a believing slave. Anyone who is unable must fast for two consecutive months[68] by way of repentance to Allah. And Allah is All-Knowing, All-Wise.