Hadith 2581
Narrated Imran ibn Husayn: The Prophet ﷺ said: There must be no shouting or leading another horse at one's side. Yahya added in his tradition: When racing for a wager.
Hadith 2582
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.