Sahih Bukhari
Fighting for the Cause of Allah (Jihaad)
Volume: 004 / Book Number: 052 / Hadith Number: 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."