Abu Dawud
Jihad
Book Number: 008 / Hadith Number: 2536
Narated By Utbah ibn AbdusSulami : Utbah heard the Apostle of Allah (pbuh) 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.