Sahih Muslim | Book 25 | Chapter 4

Narrated by Abu Huraira
Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: The vilest name in Allah's sight is Malik al-Amidh (King of Kings). The narration transmitted on the authority of Shaiba (contains these words): There is no king but Allah, the Exalted and Glorious. Sufyan said: Similarly, the word Shahinshah (is also the vilest appellation). Ahmad b. Hanbal said: I asked Abu 'Amr about the meaning of Akhna. He said: The vilest.

Narrated by Abu Huraira
Abu Huraira reported from Allah's Messenger (may peace be upon him) so many ahadith and one of them was this that Allah's Messenger (may peace be upon him) said: The most wretched person in the sight of Allah on the Day of Resurrection and the worst person and target of His wrath would of the person who is called Malik al-Amlak (the King of Kings) for there is no king but Allah.