[The Ruling on Washing and Praying over One Who Died While Being an Anthropomorphist—and What to Do]

The answer: What is incumbent upon you, O questioner, is to advise your father and urge him to repent and leave those corrupt beliefs; he is the most entitled of people to sincere counsel, admonition, and guidance. Repeat that to him with gentleness and forbearance—not with rebuke and censure—for that is among the greatest forms of dutifulness and connection. Do not despair, even until the end of his life.
If he does not respond, does not repent, and dies persisting in his creed, then bury his carcass without washing and without prayer. This is because of His saying, Exalted is He, regarding the hypocrites: “And do not pray [the funeral prayer] over any of them who has died ever, nor stand at his grave.” [al-Tawbah:84] And His saying, Exalted is He: “It is not for the Prophet and those who have believed to ask forgiveness for the polytheists—even if they were relatives—after it has become clear to them that they are companions of the Blaze. And the request of Abraham for forgiveness for his father was only because of a promise he had made to him; but when it became clear to him that he was an enemy to Allah, he disassociated himself from him …” [al-Tawbah:113–114].
If the heirs of this deceased—those who share his beliefs—are present, then do not come between them and him if they wish to wash him and pray over him; they have a greater right to him than you do, O questioner. The hypocrites are allies of one another; he is of them and they are of him.
Yes: if you fear and think that, should you refrain from washing your father and praying over him, you will be met with people’s blame—censure, reproach, and violation of your honor—and that this would become a means of harm to you, then such anticipation and fear is an excuse for washing your father, shrouding him, and praying over him.
In doing so, intend to avert harm, not to honor or exalt the deceased, and do not seek forgiveness for him. Al-Ḥusayn b. ʿAlī, peace be upon them both, prayed over the governor of Madinah, who was unjust; that was to be safe from the harm of Banū Umayyah. Zayd b. ʿAlī, peace be upon them, said—as in al-Majmūʿ: “Do not pray over the Murjiʾah, nor the Qadariyyah, nor over one who declared war against the Household of Muḥammad—unless you find no way out of it.”
Source : Min Thimār al-ʿIlm wa al-Ḥikmah vol.1