Bai'at or Bay'ah (; pledge, initiation; literally a "sale" or a "transaction") is an Islamic practice of declaring on oath, one's allegiance to a particular leader. In an Islamic religious context, this oath is the standard procedure of pledging allegiance to a religious leader. It is known to have been practiced by the Islamic prophet Muhammad and his successors (caliphs) after him with those wishing to join the Islamic community. Within the Sufi tradition the term is used to refer to the process of initiation into a Sufi order with the idea of commending oneself to a spiritual master in exchange for the spiritual and moral guidance imparted by him. The Bay'ah is a practice that also forms a notable feature within Ahmadiyya Islam. Following the death of a Caliph, the leader of the Community, a pledge of allegiance is taken by the newly chosen Caliph from members of the Community based upon this prophetic model and the bay'ah is the standard procedure for formally joining the Ahmadiyya Muslim Community.