Musannaf Ibn Abi Shayba 28:94

'Affan narrated to us, he said: Hammad ibn Salamah narrated to us, from Humayd, from al-Hasan, from 'Imran ibn Husayn, he said: The Messenger of Allah (may Allah bless him and grant him peace) said: "There is no jalab (bringing horses or camels to the place of the race or sale) and no janab (the person who accompanies the horse or camel to the place of the race or sale)."