A member of that branch of the Mohammedans to which the
   Persians belong. They reject the first three caliphs, and consider Ali
   as being the first and only rightful successor of Mohammed. They do not
   acknowledge the Sunna, or body of traditions respecting Mohammed, as
   any part of the law, and on these accounts are treated as heretics by
   the Sunnites, or orthodox Mohammedans.