Arbaʽein (Arabic: الأربعين‎, romanized: al-Arba‘īn, lit. 'forty'), Chehellom (Persian: چهلم‎, "the fortieth day") is a religious observance that occurs forty days after the Day of Ashura. It commemorates the martyrdom of Husayn ibn Ali, the grandson of Muhammad, who was martyred on the 10th day of the month of Muharram. Husayn ibn Ali and 71 of his companions were martyred by Ubayd Allah ibn Ziyad's army in the Battle of Karbala in 61 AH (680 CE). Numerous Islamic scholars have gathered collections of forty hadith, quoting from the prophet and the Imams, who followed him through the Shia sect.