What is the ruling on a son intentionally killing his father?

The crime of taking a life is one of the gravest sins. It becomes even more heinous and severe in punishment if committed by a son against his father, as it goes against sound nature and violates God's commands regarding filial piety. This entails retribution in this world if the guardians of the blood do not pardon, a severe threat of punishment in the Hereafter, and his deprivation from inheritance and blood money, for Allah, the Almighty, says: "And whoever kills a believer intentionally, his recompense is Hell, wherein he will abide eternally, and Allah has become angry with him and has cursed him and has prepared for him a great punishment."