Sahih Bukhari
Prayers (Salat)
Volume: 001 / Book Number: 008 / Hadith Number: 393
Narrated Jabir:
Allah's Apostle used to pray (optional, non-obligatory prayer) while riding on his mount (Rahila) wherever it turned, and whenever he wanted to pray the compulsory prayer he dismounted and prayed facing the Qibla.