AL-HASAN الحسن
The fifth Khalifah. The eldest son of Fatimah, the daughter of Muhammad, by her husband the Khalifah ‘Ali. Born A.H. 3. Died A.H. 49. He succeeded his father ‘Ali as Khalifah A.H. 41, and reigned about six months. He resigned the Caliphate in favor of Mu’awiyah, and was eventually poisoned by his wife Ja’dah who was suborned to commit the deed by Yazid, the son of Mu’awiyah, by a promise of marrying her, which promise he did not keep. Al-Hasan had twenty children, fifteen sons and five daughter, from whom are descended one section of the great family of Sayids, or Lords, the descendants of the Prophet. The history of al-Hasan, together with the tragical death of his brother al-Husain, form the plot of the miracle play of Muharram. [HUSAIN, MUHARRAM, SAIYID.]

Based on Hughes, Dictionary of Islam