The tradition and the process of oral narrations in the production, preservation and transportation of the materials and historical information that led to the emergence of the Islamic historiography is a fundamental issue in the Islamic historiography. In fact, the most important source of writing and compiling the historical texts of the early Islamic centuries is the verbal data that has been based on the narrations of the narrators. Due to the oral nature of a large part of the historical information and its gradual registration and editing from one hand, and some factors such as forgery, distortion, and conflict of narrations from the other hand, the validity of the historical sayings, i.e. oral narratives, is the main issue of this research. The first and most comprehensive evaluation criterion for the oral narrations is the sermon of Imam Ali (A.S) in which by dividing the traditions and narrations of the narrators into four groups has criticized the people according to their characteristics. Using a critical – analytical method, this research tries to explain the concept of oral tradition and its role in the Islamic historiography. Validation criteria for the historical narratives and narrators from the point of view of Imam Ali (A.S) were also considered.