Eid al-Adha is a religious holiday celebrated by Muslims worldwide to honor the willingness of the prophet Abraham to sacrifice his young first-born Ishmael as an act of submission to God’s command and his son’s acceptance to being sacrificed, before God intervened to provide Abraham with a Lamb to sacrifice instead. In the lunar Islamic calendar, Eid al-Adha falls on the 10th day of Dhu al-Hijjah and lasts for four days. In the international Gregorian calendar, the dates vary from year to year, drifting approximately 11 days earlier each year. Eid al-Adha celebrations start after the descent of the Hajj from Mount Arafat, a hill east of Mecca. Ritual observance of the holiday lasts until sunset of the 12th day of Dhu al-Hijjah. Eid sacrifice may take place until sunset on the 13th day of Dhu al-Hijjah.