Husein (hōsĪnˈ) [key] or Husayn –sānˈ, c.626–680, Muslim leader, second son of Ali and Fatima (daughter of Muhammad). With the assassination of his father in 661 and the acquiescence of his brother Hasan, the caliphate passed out of the Alid family, although many continued to support the claims of the sons of Ali. On the death of Hasan, Husein tried to make good his own claim, but he proved irresolute in crises. Finally he did lead an insurrection, but he and his band were massacred by the Umayyads at Karbala. The day of this defeat, the 10th of Muharram in 61 A.H. (Oct. 10, 680), known as Ashura, became the great holy day of the Shiites, who uphold the legitimacy of the Alid claims. They commemorate the day with an extensive mourning ritual that culminates in the performance of martyrdom plays. The tomb of Husein at Karbala, Iraq, is a holy place of pilgrimage. His name also appears as Hussein and Husain.