Sahih Muslim
The Book on Government (Kitab Al-Imara)
Book Number: 020 / Hadith Number: 4610
It has been narrated on the authority of Ibn 'Umar that the Messenger of Allah (may peace be upon him) had a race of the horses which had been especially prepared for the purpose from Hafya' to Thaniyyat al-Wada' (the latter being the winning post), and of those which had not been trained from Thaniyya to the mosque of Banu Zuraiq, and Ibn Umar was among those who took part in this race.