Is it permissible to rule for execution as a discretionary punishment (ta'zir) for a son who kills his father, if qisas (retaliation in kind) is not obligatory due to the pardon of some of the guardians (awliya')?

The default is that killing as a discretionary punishment (ta'zir) is impermissible, due to the generality of the verse prohibiting taking a life, and the hadith: "The blood of a Muslim person is not lawful except for one of three [reasons]." However, some jurists have permitted killing as a discretionary punishment in specific cases, such as killing a Muslim spy, or someone whose corruption is widespread and cannot be stopped except by killing, like someone who divides the Muslim community. Accordingly, if the son who killed his father is among those corrupt individuals whose evil cannot be stopped except by killing, then he is to be killed. As for merely killing his father, it does not permit killing him as a discretionary punishment if the blood relatives pardon him.