Abu Nu'aym said: Abd al-Malik bin Ata al-Amiri al-Bakka'i brought out before us a document of the Prophet (peace and blessings be upon him) which he had written for them (his tribe), and said to us: Write it down; and he did not dictate it to us. He claimed that the grandson (daughter's son) of al-Fuja'i narrated to him (that it read): This is a document from Muhammad, the Messenger of Allah (peace and blessings be upon him), to al-Fuja'i and those of his followers who accepted Islam: whoever establishes the prayer, gives the zakah, obeys Allah and His Messenger, pays the fifth (khums) of the spoils, helps the Prophet of Allah, calls witnesses to his Islam, and separates from the polytheists, then he is safe under the protection of Allah and of Muhammad (peace and blessings be upon him).
Hadith Referenceالمعجم الكبير للطبراني / باب الفاء / 15921