Sayyiduna Abu Hurayrah (may Allah be pleased with him) narrated that the Messenger of Allah (peace and blessings be upon him) said: "Spoils of war were not lawful for those before us; Allah Almighty saw our weakness and helplessness and made them wholesome for us."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الفيء والغنيمة / 12706