Is it permissible to kill or strike someone who insulted your father?

It is legislated for one whose father has been insulted to respond by denying the insult and mentioning his father's virtues, because the Prophet, peace and blessings be upon him, said: "Help your brother, whether he is an oppressor or oppressed." It is also permissible to respond with an insult, because insulting the father involves insulting his child. However, if he is assaulted physically, it is legislated to repel the aggressor with what deters him. It is not permissible to intentionally kill him unless that is the only way to repel him. Repulsion should be by the least harmful means first. If the aggressor dies without the intention of killing him, there is nothing upon the defender.