Sahih Muslim Book 20, Hadith Number 4691.

Chapter : The reward of one who fought and got his share of the booty and of one (who fought) but did not get any booty.

It has been narrated on the authority of Abdullah b. Amr (through a different chain of transmitters) that the Messenger of Allah (may peace be upon him) said: A troop of soldiers, large or small, who fight (in the way of Allah), get their share of the booty and return safe and sound, receive in advance two-thirds of their reward (only one-third remaining to their credit to be received in the Hereafter); and a troop of soldiers, large or small, who return empty-handed and are afflicted or wounded, will receive their full reward (in the Hereafter).