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"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 Allaah, And Allaah is Ever All-Knowing, All-Wise." [An-Nisaa' (4):92]

Narrated Abu Burda's father:

Allah's Apostle said "Three persons will have a double reward:

1. A Person from the people of the scriptures who believed in his prophet (Jesus or Moses) and then believed in the Prophet Muhammad (i .e. has embraced Islam).
2. A slave who discharges his duties to Allah and his master.
3. A master of a woman-slave who teaches her good manners and educates her in the best possible way (the religion) and manumits her and then marries her."

[The Book of Knowledge Volume 1, Book 3, Hadeeth 97]