Abu Sa'id al-Khudri reported the Prophet as saying, "The one who has been most generous to me with his companionship and property is Ab Bakr[*], and if I were to take a friend I would take Abu Bakr as a friend, but we have the brotherhood and love of Islam. No opening into the mosque must be left but that of Abu Bakr." A version has "If I were to take a friend other than my Lord, I would take Abu Bakr as a friend."
*After giving Abu Bakr with the nominative, it says Bukhari read Aba Bakr. That would be more usual, as it follows inna, but see p.18.
(Bukhari and Muslim.)