What is the ruling on exacting retribution from a father's murderer after his release from prison, and what is the punishment for intentionally stabbing a person with a knife, and is it considered attempted murder?

It is permissible to repel an attacker when he assaults, using whatever prevents him, even if it leads to his death, because he is an aggressor. If the aggressor is killed, there is no blame on the one who killed him. If the one being assaulted is killed, he is a martyr.

Outside of the time of aggression, it is not permissible to kill him except by the ruler or his deputy. It is not permissible for the victim's guardian to exact retribution; rather, the matter should be referred to the authorities, because retribution (qisas) and the implementation of hudud (punishments) are prerogatives of those in authority.

Stabbing a person with a knife intentionally and unjustly is forbidden, and its punishment is qisas after the wounds heal, unless the wronged party pardons. This is not carried out except by the ruler or his deputy, and the qisas must be commensurate with the crime. It is obligatory to wait for the victim to recover to determine the extent of the injury.