What was the starting date for the Muslim calendar according to the Prophet's companions, instead of the day the Prophet (saw) was sent as an Apostle or the day of his death?
 Narrated Sahl bin Sa`d:                     The Prophet's companions did not take as a starting date for the Muslim calendar, the day, the Prophet had been sent as an Apostle or the day of his death, but the day of his arrival at Medina.