Who poisoned Al-Hasan ibn Ali, may Allah be pleased with them both?

It has been narrated that Al-Hasan (may Allah be pleased with him) died of poisoning, and there is disagreement about who poisoned him. Some said it was Mu'awiyah (may Allah be pleased with him), others said Yazid ibn Mu'awiyah, and still others said it was his wife. None of these claims are substantiated.

Ibn Taymiyyah mentioned that the claim of those who accused Mu'awiyah of poisoning Al-Hasan is not supported by legal evidence, a reliable confession, or an undeniable narration. He stated that the death of someone poisoned is not hidden, but it is said that his wife poisoned him, and the most that can be conjectured is that Mu'awiyah sent for her and commanded her to do so. It is also possible that she poisoned him for another reason. Ibn Taymiyyah then clarified that Al-Hasan's father-in-law, Al-Ash'ath ibn Qays, died about ten years before Al-Hasan, so how could he order his daughter to poison Al-Hasan?

Abu Bakr ibn Al-Arabi criticized the story of Mu'awiyah poisoning him.

Ibn Kathir said that the narration stating Yazid ibn Mu'awiyah sent to Ja'dah bint Al-Ash'ath to poison Al-Hasan is not authentic, and its lack of authenticity concerning his father Mu'awiyah is even more evident.

Ibn Kathir mentioned that Al-Hasan refused to name the one who administered the poison, saying to Al-Husayn: "O my brother, this worldly life is but fleeting nights; leave it until I meet him and I at Allah's presence."

Furthermore, Al-Dhahabi's account of his death indicates that he (may Allah have mercy on him) was not certain about who poisoned him. May Allah have mercy on Al-Hasan and be pleased with him.