The Prophet (ﷺ) used to make lean by training horses which he employed in the race.
Sunan Abi Dawud Book 15, Hadith 100
← Previous Hadith ‘Abd Allah bin Umar said “The Apostle of Allaah(ﷺ) held race between the horses which had been made lean by training from Al Hafya’. The goal was Thaniyyat Al Wada’ and he held a race between the horses Banu Zuraiq and ‘Abd Allaah was one of the racers.

Sunan Abi Dawud Book 15, Hadith 99 Next Hadith → The Prophet (ﷺ) used to hold a race between horses and kept the one in the fifth year at a long distance.

Sunan Abi Dawud Book 15, Hadith 101