To overcome the confusion, Caliph Omar finally decided to introduce the Islamic Calendar and asked the people for their opinions and suggestions on the matter. Consequently various historical events, including the year when the Prophet was born, the year of the Prophethood, the time of Migration and the time when the Prophet had died, were proposed by the people.
http://ummid.com/news/2011/November/27.11.2011/islamic_calendar_new_yr_2011.htm
http://ummid.com/news/2011/November/27.11.2011/islamic_calendar_new_yr_2011.htm
