The Book Pertaining to the Merits of the Companions (Allah Be Pleased With Them) of the Holy Prophet (May Peace Be Upon Him) hadith Sahih Muslim

'Abdullah b. Mas'ud reported Allah's Messenger (may peace be upon him) as saying: If I were to choose a bosom friend I would have definitely chosen Abu Bakr as my bosom friend, but he is my brother and my companion and Allah, the Exalted and Gliorious. has taken your brother and companion (meaning Prophet himself) as a friend.