What is the ruling on one who, after his father's death, curses him and prays that he be denied mercy and forgiveness?

Invoking a curse of lack of mercy upon one's deceased father is among the most egregious forms of disobedience (ʿUqūq ), and it contradicts the words of Allah Almighty: "And say, 'My Lord, have mercy upon them as they brought me up when I was small,'" and the words of the Prophet, peace and blessings be upon him, regarding showing righteousness to one's parents after their death by praying for them, seeking forgiveness for them, fulfilling their pledges, maintaining kinship ties, and honoring their friends. The perpetrator of such an act must repent and seek forgiveness.