Sahih Muslim
The Book on Government (Kitab Al-Imara)
Book Number: 020 / Hadith Number: 4628
It has been narrated on the authority of Abu Huraira who said: Allah has undertaken to provide for one who leaves his home (only) to fight for His cause and to affirm the truth of His word; Allah will either admit him to Paradise or will bring him back home from where he had come out, with his reward and booty.