At this point it would be worthy to note as to why and when our Hijri calendar began. It was a custom of the Arabs that they would name the year according to any important incident which took place that year. For example, the year in which Makkah was attacked by Abrahaa who came to destroy the Holy Ka’bah, is called Aam ul Feel, meaning the year of Feel (Feel are the birds sent by Allah Ta’lah to destroy Abrahaa and his army). The year in which Hazrat Khadija RadiyAllahu Anha and Janab Abu Taalib died is remembered as Aam ul Huzn (the year of mourning). But there was no number or name to each year which of course caused a lot of confusion.
In his era, the second Caliph, Hazrat Umar Farooq e Aazam RadiyAllahu Anhu received a letter in which the month was mentioned but not the year. This caused him to call a meeting with the other companions so that this confusion could be ended for ever and so that Islamic history could be preserved correctly. They decided that the year should start with an important event. Hazrat Ali RadiyAllahu Anhu advised that the most important even in the lifetime of RasoolAllah Sallallahu Alaihi wa Sallam was his ‘hijrah’ that is migration from Makkah to Madinah. They all unanimously agreed that the Islalmic year should start from the day of migration. But there was a glitch. The first month should be Muharram and the migration did not take place in that month. But Hazrat Usman Gani RadiyAllahu Anhu came up with a simple solution to leave Muharram as the first month and backdate the beginning of the Hijri year to the day of migraton.
Thus the Hijri calendar came into effect on 20th Jamadil Aakhir 21 Hijri corresponding to 9th July 638 AD. This shows how important the life of RasoolAllah Sallallahu Alaihi wa Sallam was in the eyes of the companions and also the significance of establishing an Islamic system, even though a calendar did exist in those days, they established an Islamic calendar.
