Musnad Ahmad 1007:45

Hassan ibn Musa narrated to us, Ibn Lahi'ah narrated to us, and Yahya ibn Ishaq said: Ibn Lahi'ah informed us—Hassan said in his narration: Yazid ibn Abi Habib narrated to us, from Ali ibn Rabah, from Abu Qatadah, from the Messenger of Allah (peace and blessings of Allah be upon him), who said: "The best of horses is the black one, with a white blaze on its forehead, a white mark on its upper lip, and white markings on three legs, with the right hind leg left free. If it is not black, then a bay horse with these same markings."