Hazrat Abu Hurairah (radhiyallahu ‘anhu) reports that Rasulullah (sallallahu ‘alaihi wasallam) said, “There is no person who we have not repaid for the wealth he has given us (for the cause of deen) besides Abu Bakr (radhiyallahu ‘anhu), as his kindness upon us is so much that we cannot repay him. Instead, Allah Ta‘ala will repay him fully on the Day of Qiyaamah. No person’s wealth benefited me (in the cause of deen) as much as the wealth of Abu Bakr (radhiyallahu ‘anhu) had benefited me. If I had to take anyone as my khaleel (bosom friend), then I would have surely taken Abu Bakr (radhiyallahu ‘anhu) as my bosom friend. Know well that your companion (i.e. Rasulullah (sallallahu ‘alaihi wasallam)) is the khaleel of Allah Ta‘ala (i.e. the close friend of Allah Ta‘ala).” (Sunan Tirmizi #3661)
Note: The word ‘khaleel’ refers to a friend whose love and friendship has permeated the recesses of the heart, in such a manner that the heart cannot contain such love for anyone else. Rasulullah (sallallahu ‘alaihi wasallam) had reserved this special love in his heart for Allah Ta‘ala alone.