Sahih al-Bukhari 3727
صحيح البخاري#3727SahihNarrated Sa`d bin Abi Waqqas:No man embraced Islam before the day on which I embraced Islam, and no doubt, I remained for seven days as one third of the then extant Muslims
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: 62:74