Sahih Muslim Book 20, Hadith Number 4614.

Chapter : Great benefit in the forelocks of the horses.

It has been narrated on the authority of Jarir b. Abdullah who said: I saw that the Messenger of Allah (may peace be upon him) was twisting the forelock of a horse with his fingers and he was saying: (A great) benefit. i.e. reward (for rearing them for Jihad) and spoils of war, has been tied to the forelocks of horses until the Day of Judgment.