Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) says that on the day of Khaybar the Messenger of Allah (peace and blessings be upon him) forbade eating the meat of domestic donkeys, forbade intercourse with pregnant women until they give birth, forbade (eating) every fanged beast of prey, and forbade selling the khumus (one-fifth) before it is divided. In another place he said: "He forbade buying the spoils of war before they are divided."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18303