Sahih Al Bukhari 1: Chapter 4, Hadith 144

(144) While urinating or defecating, never face the Qiblah except when you are screened by a building or a wall or something like that

حَدَّثَنَا آدَمُ، ‏‏‏‏‏‏قَالَ:‏‏‏‏ حَدَّثَنَا ابْنُ أَبِي ذِئْبٍ، ‏‏‏‏‏‏قَالَ:‏‏‏‏ حَدَّثَنَا الزُّهْرِيُّ، ‏‏‏‏‏‏عَنْ عَطَاءِ بْنِ يَزِيدَ اللَّيْثِيِّ، ‏‏‏‏‏‏عَنْ أَبِي أَيُّوبَ الْأَنْصَارِيِّ، ‏‏‏‏‏‏قَالَ:‏‏‏‏ قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ:‏‏‏‏ "إِذَا أَتَى أَحَدُكُمُ الْغَائِطَ فَلَا يَسْتَقْبِل الْقِبْلَةَ وَلَا يُوَلِّهَا ظَهْرَهُ، ‏‏‏‏‏‏شَرِّقُوا أَوْ غَرِّبُوا".

SAHIH HADITH:

Narrated Abu Aiyub Al-Ansari: Allah's Apostle said, If anyone of you goes to an open space for answering the call of nature he should neither face nor turn his back towards the Qibla; he should either face the east or the west.

REFERENCE:

Sahih Al Bukhari 1: Chapter 4, Hadith 144