Eating of horse meat is lawful. It was narrated by Imam Bukhari and Muslim on the authority of Jabir who said:

‘On the Day of Khaibar, the Messenger of Allah (ﷺ) prohibited eating the flesh of domestic asses, but permitted horse flesh.’

There other numerous authentic Hadiths pointing to the fact that companions were eating horse meat. Among them was the Hadith narrated by Asma’ bnt Abubakr, may Allah be pleased with them, from the authentic Hadith of Bukhari and Muslim, she said : We slaughtered a horse in the era of prophet of Allah, may Allah’s peace and blessings be upon him, and we ate it. In another narration: “And we were in Madina”.  

Among those who make resolution on the eating of horse meat are Shuraih Al-Qadi, Hassan Al Basri, ‘Ataa’, Sa’eed bn Jubayr, Layth bn Sa’ d, Sufyaan Al-Thaory, Abu Yuusuf, Muhammad bn Hassan, Abu Thaor and others. 

Abu Hanifah, Al-Awza’i and Malik held the opinion that it is detestable. But the detestation in Maliki’s view falls under makrouh tanzihi (which is not firmly detested). Also, they deduced from Sunan Abi Dawud, An-Nasaai and Ibn Majah that the the prophet, may Allah’s peace and blessings be upon him, forbids eating of horse meat, mule, and donkeys, for Allah’s, word: And [He created] the horses, mules and donkeys for you to ride and [as] adornment. And He creates that which you do not know.[Quran 16 : 8 ]

However, Shafi’ and those who agree with him said that the intent of that verse is not about legalisation or prohibition rather the point is Allah’s definition of his grace for his servants and awakening them on the perfection of His power and wisdom. 

Concerning the Hadith in which Abu Hanifah, Malik and those who agreed with them, referred to, Imam Ahmad: it doesn’t have good reference and there are two men that are not known. Thus, we cannot leave the authentic narration for a weak one. For that reason, eating of horse meat is lawful according to the strongest opinion.