Sunan Abi Dawud Book 15, Hadith 103
The Prophet (ﷺ) said: If one enters a horse with two others when he is not certain that it cannot be beaten, it is not gambling; but when one enters a horse with two others when he is certain it cannot be beaten, it is gambling.
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.
The tradition mentioned above has also been transmitted by Al Zuhri with the chain of ‘Abbad and to the same affect.
Abu Dawud said “This tradition has also been narrated by Ma’mar, Shu’aib and ‘Aqil on the authority of Al Zuhri from a number of scholars and this is the soundest one in our opinion.