When did the Muslim calendar start?
باب التَّارِيخِ مِنْ أَيْنَ أَرَّخُوا التَّارِيخَ
Sahih al-Bukhari, Book of Merits of the Helpers in Madinah (Ansaar)(view book)
Narrated Sahl bin Sad:
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.
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، حَدَّثَنَا عَبْدُ الْعَزِيزِ، عَنْ أَبِيهِ، عَنْ سَهْلِ بْنِ سَعْدٍ، قَالَ مَا عَدُّوا مِنْ مَبْعَثِ النَّبِيِّ ﷺ وَلاَ مِنْ وَفَاتِهِ، مَا عَدُّوا إِلاَّ مِنْ مَقْدَمِهِ الْمَدِينَةَ.
Classification
Narrated 'Aisha:
Originally, two Rakat were prescribed in every prayer. When the Prophet migrated (to Medina) four Rakat were enjoined, while the journey prayer remained unchanged(i.e. two Rakat).
حَدَّثَنَا مُسَدَّدٌ، حَدَّثَنَا يَزِيدُ بْنُ زُرَيْعٍ، حَدَّثَنَا مَعْمَرٌ، عَنِ الزُّهْرِيِّ، عَنْ عُرْوَةَ، عَنْ عَائِشَةَ ـ رضى الله عنها ـ قَالَتْ فُرِضَتِ الصَّلاَةُ رَكْعَتَيْنِ، ثُمَّ هَاجَرَ النَّبِيُّ ﷺ فَفُرِضَتْ أَرْبَعًا، وَتُرِكَتْ صَلاَةُ السَّفَرِ عَلَى الأُولَى. تَابَعَهُ عَبْدُ الرَّزَّاقِ عَنْ مَعْمَرٍ.