Sahih al-Bukhari 663
صحيح البخاري#663SahihNarrated Malik Ibn Buhaina:Allah's Messenger (ﷺ) passed by a man praying two rak`at after the Iqama (had been pronounced). When Allah's Messenger (ﷺ) completed the prayer, the people gathered around him (the Prophet) or that man and Allah's Messenger (ﷺ) said to him (protesting), Are there four rak`at in Fajr prayer? Are there four rak`at in Fajr prayer?
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 10:57