Sahih al-Bukhari 3956
صحيح البخاري#3956SahihNarrated Al-Bara:I and Ibn `Umar were considered too young (to take part) in the battle of Badr, and the number of the Emigrant warriors were over sixty (men) and the Ansar were over
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: 64:8