Sahih al-Bukhari 3422
صحيح البخاري#3422SahihNarrated Ibn `Abbas:The prostration in Sura-Sa`d is not amongst the compulsory prostrations, though I saw the Prophet (ﷺ) prostrating on reciting it
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: 60:94