Below is an excerpt on the history of the origin of islamic calendar. The purely lunar calendar is known as qamariya (arabic qamar means the moon). It is also known as hijri calendar from the arabic word hegira, which means emmigration. The Prophet Muhammad pbuh, did not order anything regarding islamic calendar as an administrative or civil tools for time reckoning. He only put an example on how the beginning of (certain) islamic months be ascertained.
At the time of Khulafaur Rasyidun (The Guided Leaders), administrative system of Islamic monarch was trimmed little by little., according to the current administrative system around the world., as long as the system did not break the shariâ€™a. The correspondences had been done repeatedly. But the problem was that the muslims did not have a stable counting of the years. Hence, sometimes each of them had different naming of the years. This happened during the time of caliph Abu Bakr -may Allah be pleased with him- , and several years of the reign of Umar -may Allah be pleased with him- . Thus we know the term â€˜year of Thaâ€™unâ€™, since in that year, the epidemic of Thaâ€™un occurred and spread to various regions.
Until finally, at the third year of Umarâ€™s reign, there came a letter from Abu Musa Al Ashâ€™ari -may Allah be pleased with him- a companion whom was appointed as the governor of Bashra, which content was: â€œIndeed, the letters from The Leader of the believers (Umar) often comes to us. But we donâ€™t know, when shall we carry out the instructions inside it. Once we got a letter written in the month Shaâ€™ban, but we did not know whether it was the present Shaâ€™ban or the past year.â€
When the letter reached him, Umar Ibn Khattab -may Allah be pleased with him- gathered the senior companions at once to discuss about the issue. This meeting took place in 20th of Jumadil Akhir, year 17 of Hijra. They agreed about the urgency of date establishment process as the reference of Islamic calendar, started from the establishment of the first year. Some suggested the year of birth of the Prophet -may peace and blessings of Allah be upon him- as the first year, the other suggested the year when he was assigned as the messenger of Allah, others suggested to use the Roman or Persian calendar, and some other suggestions being raised.
Finally, a decision was made based on the opinion of Ali Ibn Abi Thalib -may Allah be pleased with him- who suggested the year of the moving (hijra) of the Prophet -may peace and blessings of Allah be upon him- from Mecca to Medina, as the first year. Whereas the decision of establishment of the first month was taken from the opinion of Uthman Ibn Affan -may Allah be pleased with him-, who proposed to make the month Muharram as the first month in Islam, because such month is the beginning of year in the Arabic calendars before Islam.
Beside that, Muharram is one of the four holy months and the muslims would be just finishing their pilgrimage at that time. The establishment of Muharram as the first month of Hijra calendar was also based on the assumption that at such month, the Prophet -may peace and blessings of Allah be upon him- had not accomplished the hijra and he reached Medina before the next year Muharram. He started the hijra at the end of month Shafar, and he reached the gate of Medina on Monday, 8th Of Rabiul Awal, then he entered Medina on Friday, 12th of Rabiul Awal. The establishment of the beginning of Hijra calendar coincided the Friday, 16th of July, 622 AD.
(Taken from â€œAl-Mufasshal fi Raddi â€˜ala Syubuhati Aâ€™da Al-Islam, 5:238)
From the origin of itâ€™s naming, this calendar is well known by â€œqamaria/moon calendarâ€, because the principle or the basis of establishment of this calendar was the rotating cycle of the moon. This calendar is also named as Hijra calendar, due to the history of itâ€™s establishment was related to the hijra of the Prophet -may peace and blessings of Allah be upon him- from Mecca to Medina.