Musnad Abu Ya'la al-Mawsili 197:1

Ibrahim ibn Sa'id al-Jawhari narrated to us, Abu Usamah narrated to us, from Mujalid, from 'Amir al-Sha'bi, from 'Amir ibn Shahr, who said: Hamdan had fortified themselves in a mountain called al-Haqal, from the Abyssinians, and Allah had protected them by means of it, until the Hamdan came to the people of Persia. They remained at war until the people were exhausted by the war and the matter became prolonged for them. The Messenger of Allah (ﷺ) went forth, and Hamdan said to me, "O 'Amir ibn Shahr, you have been a companion to kings since you were [young], so will you go to this man and scout for us? If you are pleased with something for us, we will do it, and if you dislike something, we will dislike it." I said, "Yes." So I went to the Messenger of Allah (ﷺ) in Medina and sat with him. A group of people came and said, "O Messenger of Allah, advise us." He said, "I advise you to fear Allah, and to listen to the speech of Quraysh and abandon their deeds." I was satisfied with that, by Allah, from asking him, and I was pleased with his affair. Then it occurred to me to return to my people, and I passed by the Negus, for he was a friend of mine. I passed by him, and while I was sitting with him, a young son of his passed by. He asked him to read from a tablet he had with him, and the boy read it. I laughed, and the Negus said, "What are you laughing at? By Allah, it is just as it was revealed upon the tongue of 'Isa ibn Maryam: 'The curse descends upon the earth when its rulers are children.'" I said, "Because of what this boy read." So I returned, having heard this from the Prophet (ﷺ) and this from the Negus. My people accepted Islam and descended to the plain. The Messenger of Allah (ﷺ) wrote this letter to 'Umayr Dhu Maran. He said: The Messenger of Allah (ﷺ) sent Malik ibn Murarah al-Rahawi to all of Yemen, and 'Akk Dhu Khaywan accepted Islam. It was said to 'Akk, "Go to the Messenger of Allah (ﷺ) and take from him a guarantee of safety for your people and your wealth." He had a village in which there were slaves and wealth. He came to the Messenger of Allah (ﷺ) and said, "O Messenger of Allah, Malik ibn Murarah al-Rahawi came to us calling us to Islam, so we accepted Islam. I have land in which there are slaves and wealth, so write a document for me." The Messenger of Allah (ﷺ) wrote for him: "In the name of Allah, the Most Gracious, the Most Merciful. From Muhammad, the Messenger of Allah, to 'Akk Dhu Khaywan: If he is truthful regarding his land, his slaves, and his wealth, then he has the guarantee of safety, the covenant of Allah, and the covenant of Muhammad, the Messenger of Allah (ﷺ)." Khalid ibn Sa'id wrote it.