Under what conditions is the heir permitted to enforce Qisas personally with a sharp, non-poisoned sword?
Chapter on Retaliation (Qawad)
Al-Mughni
Book of Wounds
Primary text
If the sword is sharp and not poisoned, the heir is permitted to enforce Qisas if he demonstrates competence, completing the execution through strength and knowledge. This permission is based on the verse {And whoever is killed unjustly - We have certainly given his heir authority} (Quran 17:33), and the hadith stating that the family of the slain has the choice: if they wish, they kill, and if they wish, they take blood money (diyah). This is because it is a distinct right belonging to him, and he may enforce it himself if capable, similar to other rights.
Supporting text
If the heir is not competent in enforcement, the Sultan must instruct him to appoint an agent (wakil), as he is incapable of enforcing his right. If the heir claims competence, and the Sultan permits him to execute the beheading, and he severs the head completely, his right is fulfilled. If he strikes another part of the body and admits intentionally doing so, he is subject to punitive measures (ta'zir).