Sayyiduna Jabir bin Abdullah (may Allah be pleased with them both) says: On the Day of Khaybar we slaughtered horses, mules and donkeys. The Prophet (peace and blessings be upon him) forbade donkeys and mules, but he did not forbid horse meat.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19435