The Messenger of Allah ﷺ forbade the flesh of domestic asses on the day of Khaibar, but permitted horse flesh.  

نَهَانَا رَسُولُ اللَّهِ ﷺ يَوْمَ خَيْبَرَ عَنْ لُحُومِ الْحُمُرِ وَأَذِنَ لَنَا فِي لُحُومِ الْخَيْلِ  

On the day of Khaybar we slaughtered horses, mules, and assess. The Messenger of Allah ﷺ forbade us (to eat) mules and asses, but he did not forbid horse-flesh.  

ذَبَحْنَا يَوْمَ خَيْبَرَ الْخَيْلَ وَالْبِغَالَ وَالْحَمِيرَ فَنَهَانَا رَسُولُ اللَّهِ ﷺ عَنِ الْبِغَالِ وَالْحَمِيرِ وَلَمْ يَنْهَنَا عَنِ الْخَيْلِ  

The Messenger of Allah ﷺ forbade us to eat horse-flesh, the flesh of mules and of asses. The narrator Haywah added: Every beast of prey with a fang. Abu Dawud said: This view is held by Malik. Abu Dawud said: There is no harm in (eating) horse-flesh and this tradition is not practised. Abu Dawud said: This tradition has been abrogated. A body of Companions of the Prophet ﷺ had eaten horse-flesh. OF them are: Ibn al-Zubair, Fudalah bin 'Ubaid, Anas bin Malik, Asma' daughter of Abu Bakr, Suwaid bin Ghaflah, 'Alqamah; the Quraish used to slaughter them (horses) during the time of the Messenger of Allah ﷺ.  

أَنَّ رَسُولَ اللَّهِ ﷺ نَهَى عَنْ أَكْلِ لُحُومِ الْخَيْلِ وَالْبِغَالِ وَالْحَمِيرِ زَادَ حَيْوَةُ وَكُلِّ ذِي نَابٍ مِنَ السِّبَاعِ