Prayer (Kitab Al-Salat): Detailed Rules of Law about the Prayer during Journey
Dawud :: Book 4 : Hadith 1221
Narrated Anas ibn Malik:
When the Apostle of Allah (peace_be_upon_him) was on a journey and wished to say voluntary prayer, he made his she-camel face the qiblah and uttered the takbir (Allah is most great), then prayed in whatever direction his mount made his face.