Sahih Bukhari Volume 8, Book 73, Hadith Number 225.

Narated By Abu Huraira : The Prophet said, “The most awful (meanest) name in Allah’s sight.” Sufyan said more than once, “The most awful (meanest) name in Allah’s sight is (that of) a man calling himself king of kings.” Sufyan said, “Somebody else (i.e. other than Abu Az-Zinad, a sub-narrator) says: What is meant by ‘The king of kings’ is ‘Shahan Shah.”