It is reported from Al-Shaʿbī – Allāh have mercy on him – that he said:

ʿAbdul-Malik [ibn Marwān, the Khalīfah] once sent me to the king of the Romans, and I stayed with him for a number of days. When I wanted to leave, he asked me, "Are you from the House of [your] king (his family)?" I replied, "I am just a man from the Arabs." He gave me a parchment and said, "Deliver this to your companion (the Caliph)." When ʿAbdul-Malik had read it, he said to me, "Do you know what it says?" I replied, "No." He said, "It says in it, I wonder at a people who have made other than this man king over them." I said, "By Allāh, if I had known I would not have carried it to you. [The Roman king] only said this because he has not seen you." ʿAbdul-Malik said, "Rather, he envied me for having you, and was trying to incite me to kill you." This reached the Roman king; and when it did, he said, "I wanted nothing but this."

Ibn Al-ʿImād, Shadharāt Al-Dhahab 2:26