Musnad Abu Ya'la al-Mawsili 111:30

Muhammad ibn Jami‘ al-‘Attar narrated to us, Hammad ibn Zayd narrated to us, from Ayyub, from Nafi‘, from Ibn ‘Umar, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Good is tied to the forelocks of horses."