Amr bin Shu'ayb narrates from his father, and he from his grandfather (may Allah be pleased with him), that before the verse of the spoils was revealed, the Messenger of Allah (peace and blessings be upon him) used to give people (extra) wealth; when the verse was revealed, he (peace and blessings be upon him) stopped giving in the way he used to give before. So this became (part of) the fifth of the one-fifth, and that is the share of Allah and His Messenger (peace and blessings be upon him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الفيء والغنيمة / 12947