What is the reward for the slain and the family of the victim if they pardon the killer?

The killer is accountable for three rights: a right for Allah, a right for the victim's guardians (awliya al-dam), and a right for the slain. Allah's right is waived through sincere repentance and the killer surrendering himself to the victim's guardian. The guardian's right is waived through retribution (qisas), reconciliation, or forgiveness. The right of the slain remains, for which Allah will compensate him on the Day of Judgment. The killer receives no reward for the victim's guardians forgiving their right; rather, the reward and recompense are for them.