Sayyiduna Abdullah bin Amr (may Allah be pleased with them both) said: I heard the Messenger of Allah (peace and blessings be upon him); he said: "Those who campaign in the way of Allah and obtain spoils have, as it were, taken two-thirds of their reward of the Hereafter in advance, and one-third remains for them; and if they do not obtain spoils, they will be given their full reward."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18553