Scholars
The Hijri calendar
The Hijri calendar: a lunar year of twelve months counted from the Prophet's migration to Medina in 622 — Umar ibn al-Khattab's choice in his caliphate. It holds four sacred months among them Muharram, Rajab, Dhu al-Qa'da and Dhu al-Hijja; in Ramadan Muslims fast, in Shawwal they celebrate Eid al-Fitr, in Dhu al-Hijja they make Hajj and sacrifice at Eid al-Adha. The month begins with the new crescent, so the seasons travel through the years: Ramadan comes in summer and winter, and the Hajj circles all seasons in one generation. It is Islam's oldest calendar and the one still used most for the ummah's feasts and devotions. It is today the Muslims' language of time: religious occasions are written by it and terms are counted, and if the ummah lost every other calendar it would still know its time by its Qur'an's months.