Mishkat al-Masabih #310

Abu Ayyub al-Ansari reported God’s messenger as saying, "When you go to the toilet neither face nor turn your back to the qibla , but turn towards the east or the west.” (Bukhari and Muslim.) The shaikh and imam Muhyi as-Sunna said that this tradition applies to the desert, but that in a built-up area it does not matter, on account of what is transmitted from ‘Abdallah b. ‘Umar who said, "I went up to the roof of Hafsa’s house for some purpose and saw God's messenger relieving himself facing Syria, with his back to the qibla.” (Bukhari and Muslim.)