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