Sahih al-Bukhari 5035
صحيح البخاري#5035SahihNarrated Sa`id bin Jubair:Those Suras which you people call the Mufassal, are the Muhkam. And Ibn `Abbas said, "Allah's Apostle died when I was a boy of ten years, and I had learnt the Muhkam (of the Qur'an)
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: 66:58