Musnad Ahmad 482:122

Abu Abd al-Rahman narrated to us, Ibn Lahi'ah narrated to us, Mushrih ibn Ha'an narrated to me, he said: I heard Uqbah ibn Amir saying: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "The people have submitted (as Muslims), and Amr ibn al-As has believed."