Sahih al-Bukhari 404
صحيح البخاري#404SahihNarrated `Abdullah:"Once the Prophet (ﷺ) offered five rak`at in Zuhr prayer. He was asked, "Is there an increase in the prayer?" The Prophet (ﷺ) said, "And what is it?" They said, "You have prayed five rak`at.' So he bent his legs and performed two prostrations (of Sahu)
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: 8:56