The Inception of the Islamic Calendar
According to the view of Imaam Zuhri (rahimahullah), the Islamic calendar commenced, on the instruction of Rasulullah (sallallahu ‘alaihi wasallam), from the day when he arrived in Madinah Munawwarah after the hijrah.
However, according to the more well-known view, the inception of the Islamic calendar was launched during the Khilaafah of Hazrat Umar (radhiyallahu ‘anhu).
It is reported that on one occasion, Hazrat Abu Musa Ash’ari (radhiyallahu ‘anhu) wrote to Hazrat Umar (radhiyallahu ‘anhu) saying, “Although your official correspondence and letters reach us, they are undated (hence, it is difficult for us to keep a record of the correspondence).”
Subsequently, in the 17th year after the hijrah, Hazrat Umar (radhiyallahu ‘anhu) summoned the Sahaabah (radhiyallahu ‘anhu) to discuss the issue regarding the inception of the Islamic calendar.
Some of the Sahaabah (radhiyallahu ‘anhum) proposed that the day when Rasulullah (sallallahu ‘alaihi wasallam) was blessed with nubuwwah should be the day of the inception of the Islamic calendar. Others suggested that the calendar should commence from the hijrah, while some felt that the date of Rasulullah’s (sallallahu ‘alaihi wasallam) demise should be the starting point of this calendar.
Finally, Hazrat Umar (radhiyallahu ‘anhu) made the decision stating, “The Islamic calendar should commence from the hijrah. The reason is that it was through this hijrah that truth became distinct from falsehood, and it was through the hijrah that Islam (i.e. the Muslims) began to gain honour and dominance.” This decision was met with approval by all the Sahaabah (radhiyallahu ‘anhum).
At the time of the mashwarah, some of the Sahaabah (radhiyallahu ‘anhum) had suggested that the year should commence from the month of Ramadhaan. To this, Hazrat Umar (radhiyallahu ‘anhu) replied, “No! Muharram seems to be the most appropriate month to start the calendar as people generally return from Haj in the month of Muharram.” Subsequently, they all agreed to this proposal.
Imaam Sarakhsi (rahimahullah) writes:
When Hazrat Umar (radhiyallahu ‘anhu) assembled the Sahaabah (radhiyallahu ‘anhum) to discuss the issue of stipulating the starting point of the Islamic calendar, some of the Sahaabah (radhiyallahu ‘anhum) suggested that the calendar should commence from the blessed birth of Rasulullah (sallallahu ‘alaihi wasallam). However, Hazrat Umar (radhiyallahu ‘anhu) did not approve of this view as it bore a resemblance to the way of the Christians whose calendar commences from the birth of Nabi Isa (‘alaihis salaam).
Some Sahaabah (radhiyallahu ‘anhum) suggested that the Islamic calendar should commence from the demise of Rasulullah (sallallahu ‘alaihi wasallam). Hazrat Umar (radhiyallahu ‘anhu) did not approve of this suggestion as well, as the demise of Rasulullah (sallallahu ‘alaihi wasallam) was a tragic calamity and a grave misfortune to befall this ummah, hence, it was not appropriate to commence the calendar from the date of this occurrence.
Finally, after much discussion and deliberation, all the Sahaabah (radhiyallahu ‘anhum) agreed that the Islamic calendar should commence from the hijrah. Hazrat Farooq A’zam (Hazrat Umar [radhiyallahu ‘anhu]) approved of this view as it was through hijrah that the truth (haq) became distinct and clear from falsehood (baatil), and it was after the hijrah that the sha’aair (salient symbols and ibaadaat of deen), such as the jumu’ah and the two eids, began to be openly performed and upheld.
(Extracted from Seeratul Mustafa 1/ 399-401)