Imam Malik (may Allah have mercy on him) said that Arabian and Turkish horses are all equal, because Allah said «والخيل والبغال والحمير لتركبوها» "And He created horses, mules, and donkeys for you to ride, and every rider will be given a share of only one horse (even if he owns many horses)."
Hadith Referenceصحيح البخاري / كتاب الجهاد والسير / 2864