Wood wrote that while he was studying at Old Dominion University, he was challenged to convert to Islam by his friend, Nabeel Qureshi (an American Ahmadiyya Muslim of Pakistani descent), and that he went about investigating the life of Muhammad using the earliest sources, including Ibn Ishaq's Life of Muhammad (the earliest extant biography of Muhammad); the hadith collections of Sahih al-Bukhari and Sahih Muslim (considered by Sunni Muslims to be the two most reliable or sahih collections of Muhammad's statements, actions, and example); and the History of the Prophets and Kings by Al-Tabari (one of Islam's greatest historians).