Jihad (Kitab Al-Jihad)
Dawud :: Book 14 : Hadith 2536
Narrated Utbah ibn AbdusSulami:
Utbah heard the Apostle of Allah (peace_be_upon_him) say: Do not cut the forelocks, manes, or tails of horse, for their tails are their means of driving flies, their manes provide them with warmth, and blessing is tide to their forelocks.