(6) باب عِدَّةِ أَصْحَابِ بَدْرٍ
Narrated 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 249.
Reference: Sahih al-Bukhari 3956
In-book reference: Book 64, Hadith 8
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 5, Book 59, Hadith 292