Abu Hurairah reported,
The Messenger of Allah ﷺ said, "The man who will most provoke Allah's anger on the Day of Resurrection, the vilest of men and the most detestable to Him, is a man who used to be called king of kings. There is no king but Allah." 
Ahmad 8176
Sahihوقال رسول الله ﷺ أغيظ رجل على الله يوم القيامة وأخبثه وأغيظه عليه رجل كان يسمى ملك الأملاك لا ملك إلا الله عز وجل
This is also sahih, and it is in al-Sahifa al-Mufradah, number 63. Muslim narrated it [6:174 S / 2:17 Bulaq, from the route of the Sahifa, and Bukhari did not narrate it from that route], and its meaning has already passed at 7325 from the route of the copy of Aaraj. Bukhari narrated it 486:10-487 with two chains from the narration of Aaraj.As for his saying, "There is no king but Allah," this is what is established in the copies of the Musnad, Jami al-Masanid, and al-Sahifa al-Mufradah, and it is also what is established in Sahih Muslim, the Astana edition. In the Bulaq edition it has "there is no ruler" instead of "there is no king," which, in my view, is a printing error in it. The wording "there is no ruler" is established in another narration in his book that precedes the narration of the Sahifa.