Al-Mu’tamid, the Abbasid tyrant, could not bear Imam Abu Muhammad (AS) any longer, for he saw and heard people everywhen and everywhere glorify the imam and prefer him to all the Alawids and the Abbasids. Finally, he made his mind to do away with the imam.
He assassinated him by inserting fatal poison to him.1 Poison reacted on his body, and he began suffering bitter and severe pains, while being patient, resorting to Allah.
* Taken from : The Life Of Imam Al-Hasan Al-Askari Study And Analysis By: Baqir Shareef al-Qurashi Translation by: Abdullah al-Shahin
1- Al-Irshad, p.383.