Sunni and Shia Muslims both observe Ashura, but in different ways and for different reasons. For Sunnis, Ashura commemorates God’s delivery of the Israelites from slavery. They celebrate Ashura as something akin to a feast day, but fast to be forgiven for their sins the past year. For Shia Muslims, members of the smaller branch of Islam, it is a day of mourning for the prophet Muhammad’s grandson, who was killed in the Battle of Karbala.