Ali ibn al-Husayn (Zayn al-Abidin)

Ali ibn al-Husayn ibn Ali ibn Abi Talib, known as Zayn al-Abidin and Abu al-Husayn, was the son of the martyred Imam al-Husayn. He was present at Karbala but was too ill to fight, and thus survived the massacre. He returned to Madinah and spent the rest of his life in devotion, hadith transmission, and teaching. He is revered by all Muslims for his extraordinary piety and worship — historians note he performed 1,000 rak'ahs of voluntary prayer daily. He is an important hadith transmitter from his father al-Husayn and grandfather Ali. He is considered the fourth Imam in Shi'a theology, though Sunni scholars revere him as a pious Tabi'i. He died in Madinah in 94 AH.