Muhammad bin Ishaq (may Allah have mercy on him) said: During the truce of al-Hudaybiyah, Rifa'ah bin Zayd al-Judhami came to the Messenger of Allah (peace and blessings be upon him). He gave the Messenger of Allah (peace and blessings be upon him) a slave boy as a gift, and he accepted Islam and his Islam was good. The Messenger of Allah (peace and blessings be upon him) had a letter written for him to his people, in which was: "In the name of Allah, the Most Gracious, the Most Merciful. This is a letter from Muhammad, the Messenger of Allah, for Rifa'ah bin Zayd. I have sent him to his people as a whole, and to whoever has joined them, to call them to Allah and to His Messenger. Whoever comes forward is in the party of Allah and His Messenger, and whoever turns away has safe conduct for two months." When Rifa'ah reached his people, they accepted the call and embraced Islam.
Hadith Referenceالمعجم الكبير للطبراني / باب الراء / 4547