It is not possible to ascertain the exact date of the Prophet’s birth. He is said to have been born about fifty-five days after Abraha’s attack on Makkah and in the fortieth year of reign of Chosroes Anusharwan of Persia. The birth is also said to have taken place in the year of third breaking of the Marib dam, situated some sixty miles east of Sana in Yemen and a centre of large irrigation system at the time. From these and other information, the year of the Prophet’s birth is taken as 570 or 571. Generally, the Western scholars quote the year 570 and the Eastern scholars 571.
Traditionally, the Prophet’s date of birth is celebrated on 12 Rabi I, the third month in the Muslim calendar. [A Chronology of Islamic History 570-1000 CE, Fourth Edition, TaHa Publications, 2003, p.27]