Sahih Muslim Book 4, Hadith Number 1013.

Chapter : The excellence of the prayer and the way it is begun and the excellence of Ruku’ and moderation in it and prostration and moderation in it, etc.

Ibn ‘Umar reported: The Apostle of Allah (may peace be upon him) used to say prayer towards his camel. Ibn Numair said: The Apostle of Allah (may peace be upon him) said prayer towards the camel.