Prayer effectiveness on peace of mind in Quran viewpoint

One of the most important human needs is to access to peace of mind. Thus, he/she does so many things to meet it. As a human concern, following question always raises; "what is/are the way of accessing to real peace of mind?" above question has been answered in our religious texts obviously so that real peace of mind is just accessed by memory of God and the highest level of it is prayer. The main purpose of this research is how can anyone access to peace of mind by prayer and by which method? Research method is descriptive-analytic and library references in this paper.