"Theoretically one can only receive instruction in these practices (talqîn) from an authorised teacher of the tariqa, and only after pledging a vow of obedience (bay'ah) to this shaikh. The shaikh gives his disciples permission (ijâza) to practice the tariqa: he may also authorise one or more of them to teach it to others, i.e. appoint them as his khalîfa. In this way a hierarchically ordered network of teachers may emerge. Each shaikh can show a chain of authorities for the tarekat he teaches, his silsila or spiritual genealogy. Usually the silsila reaches back from one's own teacher up to the Prophet, with whom all tarekats claim to have originated although there have been modifications along the way. A Sufi's silsila is his badge of identity and source of legitimation; it provides him with a list of illustrious predecessors and shows how he is related to other Sufis."