Sahih al-Bukhari 3858
صحيح البخاري#3858SahihNarrated Abu 'Is-haq: Sa`d bin Abi Waqqas said: None embraced Islam, except on the day I embraced it. And for seven days I was one of the three persons who were Muslims (one-third of Islam)
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: 63:83