Musnad Ahmad 25:890

Yahya ibn Adam narrated to us, Hafs ibn Ghiyath narrated to us, Dawud ibn Abi Hind narrated to us, from ‘Amr ibn Sa‘id, from Sa‘id ibn Jubayr, from Ibn ‘Abbas, who said: Dimad al-Azdi arrived in Mecca and saw the Messenger of Allah, peace and blessings of Allah be upon him, with boys following him. He said: "O Muhammad, I treat [people] for madness." The Messenger of Allah, peace and blessings of Allah be upon him, said: "Indeed, all praise is due to Allah. We seek His help and we seek His forgiveness. We seek refuge in Allah from the evils of our own selves. Whomever Allah guides, there is none to misguide him, and whomever He misguides, there is none to guide him. I bear witness that there is no god but Allah alone, with no partner, and I bear witness that Muhammad is His servant and His messenger." He said: He then said, "Repeat these words to me." He said: Then he said, "I have heard poetry, divination, and soothsaying, but I have never heard words like these. They have reached the depths of the sea. I bear witness that there is no god but Allah, and I bear witness that Muhammad is His servant and His messenger." He accepted Islam. When he accepted Islam, the Messenger of Allah, peace and blessings of Allah be upon him, said to him: "[Will you convey this] to your people?" He said: Yes, to me and to my people. He said: A detachment of the companions of the Prophet, peace and blessings of Allah be upon him, later passed by his people and took something from them—a water skin or something else. They said: "This belongs to the people of Dimad; return it." He said: So they returned it.