Musannaf Ibn Abi Shaybah 40539 — Reports on Uthman (may Allah be)

It is narrated from Hammam that a man from the People of the Book came to Sayyiduna Umar (may Allah be pleased with him) and said: "Peace be upon you, O king of the Arabs." Sayyiduna Umar said: "Do you find it this way in your Book? Do you not find it this way: first there will be a prophet, then a caliph, then the Commander of the Believers, and after that a king?" That man from the People of the Book said: "It is exactly so."