A very interesting source for investigation of the past is the collection of bibliographies of people who influenced the flow of history and the development of society. One of such people was Muhammad ibn Abd Allah, who has been recognized as the Messenger of God in Islam. Ibn Ishaq composed a biography of the legendary person that is treated as “the first full biography, or sira, of Muhammad” (Brown 69). Besides any biography itself, it is always useful for readers to analyze the sources the author has used to create the account of the life and work of a famous person to see the author’s intent and to assess his/her objectiveness. The purpose of the present paper is to analyze the sources of Ibn Ishq’s Sira and to comment on the way he makes use of the sources to prove that Muhammad is the Messenger of God. First, it is necessary to state that Ibn Ishaq made use of oral traditions relating to Muhammad’s life that existed at that time. It is worth mentioning that he created the biography about a century and a half after Muhammad’s death. This means that the gap between the life and the creation of Sira was not very wide. The thing to be mentioned relating the sources of The Life of Muhammad is that the father of the author had collected the stories of the past. It means that Ibn Ishaq’s work can be treated as a natural continuation of his fathers’ work; his tales are the basis of the biography. Ibn Ishaq often states, “My father Ishaq b. Yasar told me that he was told…” (Ibn Ishaq and Guillaume 69). In the majority of cases, he tries to define the person whom the words or the facts he presents can be attributed, such as in the following case: “Yahaya b. ‘Abbad b. Abdullah b. al-Zybayr told me that his father told him that there was a man of Lihb who was a seer” (Ibn Ishaq and Guillaume 79). However, the author’s words cannot be characterized by utmost reliability and he knows it himself. He never uses absolutely affirmative statements when he is not sure of their authoritativeness. In this case, he states, “so I have heard” (Ibn Ishaq and Guillaume 162), “it is alleged” (Ibn Ishaq and Guillaume 69), “according to what I have heard” (Ibn Ishaq and Guillaume 182). The way how Ibn Ishaq makes use of the material that is available to him can be compared with the way a seamstress is sewing a quilt, connecting little pieces (of experience, in Ibn Ishaq’s case) together. His chief aim is to reconstitute the life of Muhammad, the Messenger of God. Thus, he creates the biography trying to apply even minor details about the track of Muhammad that are known to him. Besides, when describing the events that border on mythology, such as the ascent to heaven, it is possible to see that the author is eager to sound persuasive when he says “One of whom I have no reason to doubt told me” (Ibn Ishaq and Guillaume 184). The unbelievable event of the ascent to heaven is also described with the help of the oral testimony of people he has gathered. Since the event is hard to believe, Ibn Ishaq resorts to several people he feels entitled to quote: the trustworthy man that was mentioned above, a traditionist, and Abu Sa‘id al-Khudri (Ibn Ishaq and Guillaume 185). Drawing conclusion, it is nece