Sunan at-Tirmithiy كتاب الجهاد باب ما جاء فى الرهان والسبق
ʻAbdullāh Ibn-ʻUmar once narrated, “Those horses conditioned for racing (1) were made to race by the Messenger of God, peace and blessings of God be upon him, from al-Ḥafyā’ to Thaniyyat al-Wadā‘ (2): a distance of six miles. While those which did not undergo any conditioning were made to race from Thaniyyat al-Wadā‘ to the mosque of Banū-Zurayq: a distance of one mile. I was among those racing when my horse jumped over a wall.” Footnotes: (1): This process involves feeding horses in abundance until they gain weight and become stronger. Thereafter, their food is decreased and they are placed in a room in which they are covered with a cloth, making them sweat profusely. This makes them leaner and stronger and increases their strength for racing. (2): Areas located outside Madīnah. Click on ḥadīth to read more