Sahih Muslim, Hadith 1906b

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).