Sahih Bukhari
Sahih Bukhari Volume 005, Book 057, Hadith Number 008.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 57. Companions of the Prophets
Narated By Ibn 'Abbas : The Prophet said, "If I were to take a Khalil, I would have taken Abu Bakr, but he is my brother and my companion (in Islam)."