We slaughtered a horse during the lifetime of Messenger of Allah ﷺ and ate it.  

نَحَرْنَا فَرَسًا عَلَى عَهْدِ رَسُولِ اللَّهِ ﷺ فَأَكَلْنَاهُ  

On the Day of the battle of Khaibar, Messenger of Allah ﷺ made donkey's meat unlawful and allowed the eating of horse flesh.  

نَهَى النَّبِيُّ ﷺ يَوْمَ خَيْبَرَ عَنْ لُحُومِ الْحُمُرِ وَرَخَّصَ فِي لُحُومِ الْخَيْلِ