Sahih Muslim Book 20, Hadith Number 4642.

Chapter : Merit of leaving for Jihad in the morning and evening.

It has been narrated on the authority of Abu Huraira that the Messenger of Allah (may peace be upon him) said: If some persons of my Umma (were not to undertake the hardships of Jihad), and he (Abu Huraira) then narrated the rest of the hadith and then said: A journey undertaken for jihad in the evening or morning merits a reward better than the world and all that is in it.