Sahih al-Bukhari, Hadith 3934 ⓘ
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.
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، حَدَّثَنَا عَبْدُ الْعَزِيزِ، عَنْ أَبِيهِ، عَنْ سَهْلِ بْنِ سَعْدٍ، قَالَ مَا عَدُّوا مِنْ مَبْعَثِ النَّبِيِّ صلى الله عليه وسلم وَلاَ مِنْ وَفَاتِهِ، مَا عَدُّوا إِلاَّ مِنْ مَقْدَمِهِ الْمَدِينَةَ.
also referenced under: Book 63, Hadith 160 (In-Book) & Volume 5, Book 58, Hadith 271 (USC-MSA)