Sahih al-Bukhari 473
صحيح البخاري#473SahihNarrated Ibn `Umar:A man came to the Prophet (ﷺ) while he was delivering the sermon and asked him how to offer the night prayers. The Prophet (ﷺ) replied, 'Pray two rak`at at a time and then two and then two and so on and if you are afraid of dawn (the approach of the time of the Fajr prayer) pray one rak`a and that will be the witr for all the rak`at which you have prayed." Narrated 'Ubaidullah bin `Abdullah bin `Umar: A man called the Prophet (ﷺ) while he was in the mosque
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: 8:121