Al-Biruni of Kwarizm (973 – c. 1050 ce), the great Islamic historian, answered this question as follows¹ (the translation by Edward Sachau has been slightly modernized):
“The circumstances under which this very point was adopted as an epoch, and not the time when the Prophet was either born or entrusted with his divine mission or died, were the following:
“Maimûn ben Mihrân relates,
that Omar ben Alkhattâb, when people one day handed him a check payable in the month Sha’bân, said:– “Which Sha’bân is meant? that one in which we are or the next Sha’bân?” Thereupon he assembled the Companions of the Prophet, and asked their advice concerning the matter of chronology, which troubled his mind. They answered: “It is necessary to inform ourselves of the practice of the Persians in this respect.” Then they fetched Hurmuzân, and asked him for information. [Hurmuzân describes the Persian and Greek eras.] Then Omar spoke to the Companions of the Prophet: “Establish a mode of dating for the commerce and communication of the people.” Now some said, “Date according to the era of the Greeks, for they date according to the era of Alexander.” Others objected that this mode of dating was too lengthy, and said, “Date according to the era of the Persians.” But then it was objected that as soon as a new king arises among the Persians he abolishes the era of his predecessor. So they could not come to an agreement.
that ‘Abû-Mûsâ Al′ash‘ari wrote to Omar ben Alkhattâb: “You send us letters without a date.” Omar had already organized the registers, had established the taxes and regulations, and was in want of an era, not liking the old ones. On this occasion he assembled the Companions and took their advice. Now the most authentic date, which involves no obscurities nor possible mishaps, seemed to be the date of the flight of the Prophet, and of his arrival at Medina on Monday the 8th of the month Rabi’ I, whilst the beginning of the year was a Thursday. Now he adopted this epoch, and fixed thereby the dates in all his affairs. This happened ah 17.
“The reason why Omar selected this event as an epoch, and not the time of the birth of the Prophet, or the time when he was entrusted with his divine mission, is this, that regarding those two dates there existed such a divergency of opinion, as did not allow it to be made the basis of something which must be agreed upon universally.
“Further he (Alsha’bi) says:
People say that he was born in the night of Monday the 2nd, or the 8th, or the 13th of Rabi I.; others say that he was born in the 46th year of the reign of Kisrâ Anôshirwân. In consequence there is also a difference of opinions regarding the length of his life, corresponding to the different statements regarding his birth. Besides, the single years were of different lengths, some having been intercalated, others not, about the time when intercalation was prohibited. Considering further that after the Flight, the affairs of Islam were thoroughly established, while heathenism decreased, that the Prophet was saved from the calamities prepared for him by the infidels of Mecca, and that after the Flight his conquests followed each another in rapid succession, we come to the conclusion that the Flight was to the Prophet, what their accession is to kings, and their taking possession of the whole sovereign power.
“As regards the well known date of his death, people do not like to date from the death of a prophet or king, except the prophet be a liar or the king an enemy, whose death people enjoy, and wish to make a festival of; or he be one of those with whom a dynasty is extinguished, so that his followers among themselves make this date a memorial to him, and a mourning feast.”
The Chronology of Ancient Nations. An English Version of the Arabic text of the athar-ul-bakiya of alBiruni.
C. Edward Sachau, translator and editor.
London: William H. Allen and Co., 1879.
Reprinted 1983 by Hijira International Publishers, Mian Chambers, 3-Temple Road, Lahore, Pakistan.
Copyright © 2000 Sizes, Inc. All rights reserved.
Last revised: 11 March 2004.