Sahih al-Bukhari 3935
Book 63: Merits of the Helpers in Madinah (Ansaar) · Narrated by `Aisha
Arabic
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 صلى الله عليه وسلم فَفُرِضَتْ أَرْبَعًا، وَتُرِكَتْ صَلاَةُ السَّفَرِ عَلَى الأُولَى. تَابَعَهُ عَبْدُ الرَّزَّاقِ عَنْ مَعْمَرٍ.
English translation
Narrated `Aisha: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)
Reference: Sahih al-Bukhari 3935, Book of Merits of the Helpers in Madinah (Ansaar). English translation by Dr. Muhammad Muhsin Khan.