Sahih Bukhari Volume 9, Book 85, Hadith Number 74.

Narrated By Anas : Allah’s Apostle said, “Whoever possesses the (following) three qualities will have the sweetness of faith:
  1. The one to whom Allah and His Apostle becomes dearer than anything else;
  2. Who loves a person and he loves him only for Allah’s Sake; 
  3. Who hates to revert to atheism (disbelief) as he hates to be thrown into the Fire.”