Ali-Illahism is a syncretic religion which has been practiced in parts of the Luristan region in Iran which combines elements of Shia Islam with older religions. It centers on the belief that there have been successive incarnations of God throughout history, and Ali-Illahis reserve particular reverence for Ali, the son-in-law of the Islamic prophet Muhammad, who is considered one such incarnation. Various rites have been attributed as "Ali-Illahi," similarly to the Yazidis, Alawites, and all sects whose doctrine is unknown to the surrounding Muslim and Christian populations. Observers have described it as an agglomeration of the traditions and rituals of several older religions, including Zoroastrianism, historically because travelogues were "evident that there is no definite code which can be described as Ali-Illahism."