Sahih Muslim, Chapter: Purification (Kitab Al-Taharah)

I was offering my prayer in the mosque and Abdullah b. Umar was sitting there reclining with his back towards the Qibla. After completing my prayer. I went to him from one side. Abdullah said: People say when you go to the latrine, you should neither turn your face towards the Qibla nor towards Bait-ul-Maqdis. 'Abdullah said (farther): I went up to the roof of the house and saw the Messenger of Allah (may peace be upon him) squatting on two bricks for relieving himself with his face towards Bait-al-Maqdis.