(48) باب التَّارِيخِ مِنْ أَيْنَ أَرَّخُوا التَّارِيخَ
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). (IT)
Reference (IT): Sahih al-Bukhari 3935 (IT)
In-book reference (IT): Book 63, Hadith 161 (IT)
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 5, Book 58, Hadith 272 (IT)