Musannaf Ibn Abi Shayba 28:961

Waki’ narrated to us, he said: Ibn ‘Awn narrated to us, from Sa’id al-Bazzar, from Makhul, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Good is tied to the forelocks of horses until the Day of Resurrection, and their owners are aided regarding them."