Abu Dawud Book 13, Hadith Number 3021.
Narated By Amir ibn Shahr : When the Apostle of Allah (PBUH) appeared as a prophet, Hamdan said to me: Will you go to this man and negotiate for us (with him)? If you accept something, we shall accept it, and if you disapprove of something, we shall disapprove of it.
I said: Yes. So I proceeded until I came to the Apostle of Allah (PBUH). I liked his motive and my people embraced Islam. The Apostle of Allah (PBUH) wrote the document for Umayr Dhu Marran. He also sent Malik ibn Murarah ar-Rahawi to all the (people of) Yemen. So Akk Dhu Khaywan embraced Islam.
Akk was told: Go to the Apostle of Allah (PBUH), and obtain his protection for your town and property. He therefore came (to him) and the Apostle of Allah (PBUH) wrote a document for him:
“In the name of Allah, Most Beneficent, Most Merciful. From Muhammad, the Apostle of Allah, to Akk Dhu Khaywan. If he is true his land, property and slave, he has the security and the protection of Allah, and Muhammad, the Apostle of Allah. Written by Khalid ibn Sa’id ibn al-‘As.”