Most qualitative research studies examine leaders' decision-making process (DMP) patterns by using a single methodological approach. Even studies that use triangulation of approaches don't use more than one qualitative-analytical method. Although this kind of research suggests an in-depth examination of the DMP, it is incomplete. This is due to a relatively narrow point of view, i.e. a single qualitative-analytical methodology. In order to get a broader, yet an in-depth examination of leaders' DMP, this paper suggests using a combination of three qualitative-analytical methodologies, each contributing a different perspective on the DMP. First, the study will apply Applied Decision Analysis (ADA), to identify the leader's decision rule. Thereafter, we shall use Non-Cooperative Game Theory and in particular - Extensive Form, to examine how the leader's decisions are made when they take into account other players under conditions of uncertainty. Finally, the study will address cognitive psychology by using Prospect Theory, for understanding leader's degree of risk-taking or risk aversion, depending on their own framing. The case study of this paper will be the key decisions related to war and peace of the founder of Islam, the Prophet Muhammad. The results of the research suggest that the Prophet Muhammad follows the Rational Choice Rule; Furthermore, He tried to predict the behavior of his adversary to maximize his gains; and his decision-making process is characterized by the principle of Loss Aversion.