Sahih Bukhari Volume 004, Book 052, Hadith Number 046.

Narated By Abu Huraira : I heard Allah's Apostle saying, "The example of a Mujahid in Allah's cause... and Allah knows better who really strives in his cause... is like a person who fasts and prays continuously. Allah guarantees that He will admit the Mujahid in His Cause into Paradise if he is killed, otherwise He will return him to his home safely with rewards and war booty."