Musnad Ahmad 407:2

Abdullah ibn Ahmad said: Abu ‘Amir Hawtharah ibn Ashras dictated to me, saying: Hammad ibn Salamah informed me, from Abdullah ibn Uthman ibn Khuthaym, from Sa’id ibn Abi Rashid, who said: The messenger of Caesar was a neighbor of mine during the time of Yazid ibn Mu’awiyah. I said to him: "Tell me about the letter of the Messenger of Allah, peace and blessings of Allah be upon him, to Caesar." He said: "The Messenger of Allah, peace and blessings of Allah be upon him, sent Dihyah al-Kalbi to Caesar, and he wrote a letter with him to him." He then mentioned something similar to the hadith of ‘Abbad ibn ‘Abbad—and the hadith of ‘Abbad is more complete and better in the narration of the story—and he added: "The Messenger of Allah, peace and blessings of Allah be upon him, laughed when he invited him to Islam, but he refused to accept Islam, and he recited this verse: 'Indeed, you do not guide whom you like, but Allah guides whom He wills' [Al-Qasas: 56]. Then the Messenger of Allah, peace and blessings of Allah be upon him, said: 'You are the messenger of a people, and you have a right, but you have come to us while we are destitute.' Uthman ibn Affan said: 'I will clothe him in a Safuri garment,' and a man from the Ansar said: 'His hospitality is upon me.'"