Sahih Bukhari
Fighting for the Cause of Allah (Jihaad)
Volume: 004 / Book Number: 052 / Hadith Number: 104
Narrated 'Urwa Al-Bariqi:
The Prophet said, "Good will remain (as a permanent quality) in the foreheads of horses (for Jihad) till the Day of Resurrection, for they bring about either a reward (in the Hereafter) or booty (in this world."