Ḥasan b. ʿAlī b. Abī Tālib (a) (Arabic: حسن بن علي بن ابي طالب) (b.3/625-d.50/670), son of 'Ali (a) and Fatima (a), is the second Imam of the Shi'a and became caliph and imam at the age of 37. He accepted a peace treaty with Mu'awiya in 41/661. His government lasted six months and three days. He went to Medina after the peace treaty, and stayed there until he was martyred ten years later. He was buried in the Jannat al-Baqi' cemetery. Because of his responsibility of Imamate and preserving the unity of Muslims, he accepted a peace treaty with Mu'awiya. His decisions show his solemn and tolerant personality. His caliphate and peace treaty with Mu'awiya were among the most important events in his life and in early Islamic history. It demonstrated an example of unity at that time and as a moral and religious teaching, it greatly regulated Muslims and especially Shi'as throughout their history in their approach towards fundamental concepts like authority, war and peace.