Fighting for the Cause of Allah (Jihaad)

Bukhari :: Book 4 :: Volume 52 :: Hadith 65

Narrated Abu Musa:

A man came to the Prophet and asked, "A man fights for war booty; another fights for fame and a third fights for showing off; which of them fights in Allah's Cause?" The Prophet said, "He who fights that Allah's Word (i.e. Islam) should be superior, fights in Allah's Cause."