During whose caliphate was the Islamic (Hijri) calendar formally established?

Explanation

– The Islamic Hijri calendar was formally established during the caliphate of Umar (RA), who designated the year of the Prophet’s migration to Madinah, 622 CE, as the starting reference point, marking it as 1 AH.
– This calendar remains the standard lunar calendar used for religious purposes within Islam.
– For exams, remember that the Hijri calendar consists of twelve lunar months and is approximately eleven days shorter than the solar Gregorian calendar.