How do Muslims (particularly Shi'ite) prove they are descendants of the Prophet Muhammad? For example, black turbans are worn among some of Iran's religious leaders to show they are a descendant of Muhammad. Ayatollah Khomeini and the current Ayatollah, Khamenei, claim their lineage can be traced back to Muhammad. How do they prove this?
See any of the threads about how all western Europeans are descended from Charlemagne.