On forbidding that a Sultan be called Shahneshah because it means "the King of Kings" and only Allah is described as that

Riyad as-Salihin (The Meadows of the Righteous)

by Imam Nawawi

320. Chapter: On forbidding that a Sultan be called Shahneshah because it means "the King of Kings" and only Allah is described as that

1724. Abu Hurayra reported that the Prophet, may Allah bless him and grant him peace, said, "The most abased man in the sight of Allah, the Mighty and Majestic, is a man who calls himself, 'the King of Kings.'" [Agreed upon]