(Arabic; derived from ba-ya-‘a, meaning ‘to sell’ or ‘clasp hands’). A practice rooted in Arab tradition and the practice of Prophet Muhammad. It is also mentioned in the Holy Qur’an (see 48:10, 48:18, and 60:12) and defined as an oath of allegiance, an act by which a certain number of people, individually or collectively, recognise the authority of an individual. Thus, the bay‘a of a Caliph was the act by which an individual was proclaimed and recognised as the head of the Muslim State. In many Muslim traditions, the meaning of bay‘a is to offer oneself to a spiritual master, pir, murshid, or shaykh in exchange for spiritual knowledge and guidance. In Shi‘i contexts, the word is used for the oath of allegiance to the Imam by his followers. In the Shi‘i Ismaili tradition, it is the acceptance of the permanent spiritual bond between the Imam and the murid, uniting all Ismaili Muslims worldwide in their loyalty, devotion and obedience to the Imam within the Islamic concept of universal brotherhood.