Hijrah, migration or exodus, initially of the Prophet Muhammad and his companions from Mecca to Yathrib (later renamed Madinah), features prominently in the Qur’an and the teachings and Sunnah of the Prophet himself. The Prophet and his followers migrated, after thirteen years of campaign in Mecca on 1 Rabi’ al-Awwal/13 September 622 AD, arriving in Yathrib 11 days later on 24 September. The commemoration of the Hijri calendar was instituted, however, seventeen years later by the second caliph, ‘Umar ibn al-Khattab (r. 634-644). The new calendar dates from the first day of the first lunar month of the year, that is, Awwal Muharram. Although ‘Umar instituted the official era, the custom of referring to events and happenings to before or after the Hijrah originated with the Prophet himself.