Mishkat al-Masabih 20 Game and Animals Which May Be Slaughtered كتاب الصيد والذبائح 43

وَعَنْ جَابِرٍ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ نَهَى يَوْمَ خَيْبَرَ عَنْ لُحُومِ الْحُمُرِ الْأَهْلِيَّةِ وَأَذِنَ فِي لُحُومِ الْخَيْلِ

Jabir said that on the day of Khaibar God’s messenger forbade the flesh of domestic asses, but permitted horseflesh. (Bukhari and Muslim.)