Sahih Muslim
The Book on Government (Kitab Al-Imara)
Book Number: 020 / Hadith Number: 4642
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.