Chapter: When did the Muslim calendar start?

The Prophet's companions did not take as a starting date for the Muslim calendar, the day, the Prophet (ﷺ) had been sent as an Apostle or the day of his death, but the day of his arrival at Medina.

Originally, two rak`at were prescribed in every prayer. When the Prophet (ﷺ) migrated (to Medina) four rak`at were enjoined, while the journey prayer remained unchanged(i.e. two rak`at).