Sayyiduna al-Miqdam (may Allah be pleased with him) says that on the day of Khaybar the Messenger of Allah (peace and blessings be upon him) declared certain things unlawful, among them the domestic donkey. The narrator says that he (peace and blessings be upon him) said: "Soon a man, reclining on his couch while narrating my hadith, will say: The Book of Allah is sufficient for us; whatever we find in it lawful or unlawful, that is final. Beware! What the Messenger of Allah (peace and blessings be upon him) has declared unlawful is like what Allah has declared unlawful."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19468