It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both); he said: "The Messenger of Allah (peace and blessings be upon him) forbade eating the meat of donkeys, and the Messenger of Allah (peace and blessings be upon him) ordered that the meat of horses be eaten."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12765