When Muhammad was forty years old Allah sent him as a prophet of mercy to the people of the visible and of the invisible worlds, and to all mankind. With every prophet whom Allah had sent before the time of Muhammad, he had made a covenant, binding each of them to believe in the coming of Muhammad, to declare him a true apostle, to aid him against every opponent, and to testify to every man who believed in the truth of their own prophetic missions that the mission of Muhammad was still to come. They complied, according to His command, and spread the covenant of Allah to all who believed in them, so that many men who believed in the Old or the New Testament believed also in the truth of this covenant.
— “The Revelation,” from The Life of Muhammad: Apostle of Allah
Ibn Ishaq (?–ca.767) was an Arab historian whose collection of oral histories became known as Sirat Rasul Allah (“The Apostle of Allah”). While he wrote several works, his Life of the Prophet is his only extant work — although even the text for this work is a restoration from versions reportedly written by his students. The grandson of a man captured during a campaign of Muhammad’s famous military commander Khalid ibn al-Walid, Ishaq worked in Baghdad until his death.