More than 3 million Muslims from around the world traveled to Mecca this week for the hajj, the annual pilgrimage all able Muslims are called upon to perform once in their lifetime. Pilgrims take part in a series of rituals that recall events from the lives of Abraham and the prophet Muhammad. On Friday, Muslims began observing the three days of Eid al-Adha or the Festival of Sacrifice. Some sacrifice animals such as sheep or cows to recall Abraham’s willingness to sacrifice his son in obedience to God.