Musnad Ahmad 33:674

Ibrahim ibn Ishaq and Ali ibn Ishaq narrated to us, they said: Ibn al-Mubarak narrated to us, from Utbah—and Ali said: Utbah ibn Abi Hakim informed us—Husayn ibn Harmalah narrated to me, from Abu Musabbih, from Jabir ibn Abdullah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Goodness and attainment are tied to the forelocks of horses until the Day of Resurrection, and their owners are aided with them. So wipe their forelocks, supplicate for blessing for them, and put garlands on them, but do not put garlands on them with bowstrings." And Ali said: "And do not put bowstrings as garlands on them."