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 Allah. And Allah 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 Allah are upon him, and a great punishment is prepared for him.

O you who believe! When you go (to fight) in the Cause of Allah, verify (the truth), and say not to anyone who greets you (by embracing Islam): "You are not a believer"; seeking the perishable goods of the worldly life. There are much more profits and booties with Allah. Even as he is now, so were you yourselves before till Allah conferred on you His Favours (i.e. guided you to Islam), therefore, be cautious in discrimination. Allah is Ever Well-Aware of what you do.

Not equal are those of the believers who sit (at home), except those who are disabled (by injury or are blind or lame, etc.), and those who strive hard and fight in the Cause of Allah with their wealth and their lives. Allah has preferred in grades those who strive hard and fight with their wealth and their lives above those who sit (at home). Unto each, Allah has promised good (Paradise), but Allah has preferred those who strive hard and fight, above those who sit (at home) by a huge reward;

Degrees of (higher) grades from Him, and Forgiveness and Mercy. And Allah is Ever Oft-Forgiving, Most Merciful.