Fatimah bint al-Mundhir (may Allah have mercy on her) narrates from her grandmother Asma' (may Allah be pleased with her): We slaughtered a horse in the time of the Messenger of Allah (peace and blessings be upon him) and ate it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19442