Sunan an-Nasa'i 454
سنن النسائي#454SahihAbu 'Amr - meaning, Al-Awza'i - said that he asked Az-Zuhri about the prayer of the Messenger of Allah (ﷺ) in Makkah before the Hijrah to Al-Madinah. He said:"Urwah told me that 'Aishah said: 'Allah enjoined the salah upon the Messenger of Allah (ﷺ), and the first thing that He enjoined was two Rak'ahs at a time, then it was made complete four Rak'ahs while in the state of residence but the prayer when traveling remained two Rak'ahs, as it was first enjoined
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiIsnaad Sahih
In-book reference: 5:7