The Concise Oxford Dictionary of World Religions (1109 page)

An aggregation of Muslim groups, notable for esoteric teaching. They emerged historically from disputes following the death of the sixth Sh
‘a
Im
m
, Ja‘far al-S
diq. The succession should have passed to his eldest son, Ism
‘
l, but he died before his father. Nevertheless, some maintained that the authority had been transmitted to him as the first-born (and beyond him to his son). Others held that the succession should pass to Ja‘far's eldest surviving son (his third), M
s
al-K
zim. The Twelvers (
ithn
‘ashariyya
, majority Sh
‘a) chose M
s
and his successors, while those following Ism
‘