Nafi' (may Allah have mercy on him) narrates from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the course for the horses was fixed at six miles, then they were raced against each other, and the Prophet (peace and blessings be upon him) gave a prize to the winner.
This Hammad bin Sulayman is majhul (unknown).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السبق والرمي / 19769