Death of Hazrath Zain al-Abideen

He resided in Medina until his death on 25th of Muharram, 95 AH (approximately 23 October , 712).When the Bani Umayyah rulers realised the wisdom of Imam Zainul Abidin's approach to establish Islam through the memory of his father and prayers to Allah and their mistake, they decided to kill the Imam. By the instructions of Walid Bin Merwan, the governor of Medina, The Imam (A.S) was poisoned by Hisham ibn Abd al-Malik. He was buried in Jannatul Baqee', the cemetery in Madinah where other important figures of Islamic history are buried. The period of his Imaamat is 33 years.
Source; Wikepedia