4:65: Abu Musa: A man came to the Prophet and asked, A man fights for war booty; ...
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."