Jabir b. 'Abdullah reported that Messenger of Allah ﷺ prohibited eating of the flesh of domestic asses on the Day of Khaibar, and permitted the cooking of the flesh of horses. (Using translation from Muslim 1941a)
أَنَّ رَسُولَ اللهِ ﷺ نَهَى يَوْمَ خَيْبَرَ عَنْ لُحُومِ الْحُمُرِ وَأَذِنَ فِي لُحُومِ الْخَيْلِ