Sahih Bukhari
Sahih Bukhari Volume 005, Book 059, Hadith Number 291.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 59. Military Expeditions Led by the Prophet (PBUH) (Al-Maghaazi)
Narrated By Al-Bara: I and Ibn 'Umar were considered too young to take part in the battle of Badr.