Sunan Abi Dawud Book 15, Hadith 101
The Prophet (ﷺ) used to hold a race between horses and kept the one in the fifth year at a long distance.
The Prophet (ﷺ) used to make lean by training horses which he employed in the race.
while she was on a journey along with the Messenger of Allah (ﷺ): I had a race with him (the Prophet) and I outstripped him on my feet. When I became fleshy, (again) I had a race with him (the Prophet) and he outstripped me. He said: This is for that outstripping.