(70) باب فِي الْجَلَبِ عَلَى الْخَيْلِ فِي السِّبَاقِ
Qatadah said "Taking another horse behind one's horse to urge it on and taking another horse at one's side are (done) in a horse race.
Reference: Sunan Abi Dawud 2582
In-book reference: Book 15, Hadith 106
English translation: Book 14, Hadith 2576