December 27 marked "Ashura," an important day to Shiite Muslims. Ashura means "10" and is commemorated by Shia Muslims as a day of mourning for the killing of Husayn ibn Ali, the grandson of the Islamic Prophet Muhammad, at the Battle of Karbala on 10 Muharram in the year 61 AH.
Some Sunni Muslims also claim that Moses fasted on that day to express gratitude to God for liberating the Israelites from Egypt.
According to Sunni Muslim tradition, the Prophet Muhammad fasted on this day and asked other people to fast.
Reuters shared some raw video footage of the Shiite Muslims commemorating Ashura, shown below. The video might take a second or two to load.