Abdullah bin Omar, may God be pleased with them both, narrated – “The Messenger of God raced among horses, and preferred ulcers in the end.” Narrated by Abu Dawood, and its chain of transmission is correct.
And ulcers: the plural of Qarih, and the teeth of horses: in the first year around me, then a trunk, then a bend, then a quarter, then a Qarih.
The hadith indicates that five-year-old horses have a racing distance farther than younger horses; In order to equal opportunities between them.