The period of Imamah of the seventh Imam was during the rule of some of the most powerful and oppressive caliphs of the Banul ‘Abbas, such as al-Manṣūr and Harūn ar-Rashīd. Under the ruthless rule of these dictators, not only were many internal uprisings across the Muslim world crushed, but the Islamic Empire was expanded. These victories, and the wealth that they brought, gave strength to the kingdom of the Banul ‘Abbas. Unlike the time of previous Imams or the Imams to come later, the government during this time faced no serious threat to its rule. This means that they were able to pay full attention to the threat posed by the Ahlul-Bayt (a).
For this reason, scholars say that only the time period of the Imamah of Imam as-Sajjād (a) was more difficult for the Ahlul-Bayt than the Imamah of Imam al-Kāẓim. On many occasions the Imam was forced to leave Madinah, either being exiled, arrested, or due to his own decision to go into hiding. At multiple times, the caliph decided to have the Imam killed, but for one reason or another his plan was not carried out. In this dangerous situation, the tireless and firm resistance of Imam al-Kāẓim kept the Shiʻah community safe and vibrant, allowing them to not only continue their intellectual and political activities but in fact increase these activities.
In the year 179 AH, the caliph Harūn ar-Rashīd went for Hajj, intending to both arrest the Imam and also secure the oath of allegiance from the community for his two sons, Ma’mūn and Muḥammad al-Amīn. Scared of the repercussions of killing the Imam, Harūn hoped that he would be able to pressure or bribe the Imam to surrender to him by throwing him in jail. At Harūn’s order, the Imam was arrested and dragged out of the mosque of the Holy Prophet (s) when he was busy engaged in prayer. The people of Madinah cried at seeing the Imam treated in this manner. The Imam was sent to Basra and imprisoned there. During this time, he was only allowed out of the prison to perform wuḍū’ and to receive food. It is narrated that he spent most of his time busy in worship, especially in the state of sajdah. He would be in the state of sajdah from sunrise till the time of ẓuhr, such that people who looked at him in this state mistook him for a cloth that had been spread on the floor!
From the prison in Basra, the Imam was transferred to other prisons in the city of Baghdad. The last prison he was sent to was that of someone named as-Sindī bin Shāhak. As-Sindī was the one who eventually fed the Imam poisoned dates on the order of Harun. The famous opinion regarding the date of the martyrdom of the Imam is the 25th of Rajab in the year 183 AH.
After his death the authorities left his pure body on a bridge in Baghdad, open for the public to see. A public announcement was made: “This is the Imam of the rāfiḍah (those who reject faith, a derogatory term used for the Shīʻah)”. In an attempt to hide the fact that he had been killed, people were called to see how his body had no sign of any wound or being choked. The Imam was buried in the graveyard of the Quraysh, today the blessed shrine known as Kāẓimayn in Baghdad.