Arba'een, also known as the Martyrdom of Husayn ibn Ali, is a significant Shia Muslim religious observance that occurs forty days after the Day of Ashura, typically falling on the 20th or 21st day of the Islamic month of Safar. It commemorates the martyrdom of Husayn ibn Ali, the grandson of the Prophet Muhammad, who was killed in the Battle of Karbala in 680. This observance is particularly prominent in Iran, where it is recognized as a public holiday, but it is also observed worldwide, with millions of Muslims participating in the pilgrimage to Karbala, Iraq. Pilgrims visit the Imam Husayn Shrine, which marks his burial site, to honor his memory. The observance culminates a traditional forty-day mourning period that begins with Ashura, and while primarily a Shia event, it also sees participation from Sunni Muslims.