Imam Husayn ('a) narrates the story of prophet Yaḥya ('a)’s martyrdom/ Imam Husayn ('a) predicts his own martyrdom/the promise of the advent of Imam Mahdi ('a) who will avenge Imam Husayn ('a)/the arrival of Umar ibn Saʿd in Karbala/Umar ibn Saʿd’s letter to Ibn Ziad