JAMI AL-TIRMIDHI

Concerning disallowance to face the qiblah while relieving oneself
  (8)

 Sayyidina Abu Ayyub Ansari narrated that Allah's Messenger (SAW) said, "When you go
to the toilet, do not face the qiblah while passing stool or urine nor turn your backs to it,
but turn to the east or west."
Abu Ayyub (RA) said, "When we arrived in Syria, we found their privies built facing qiblah,
so we would turn away from that and would seek Allah's forgiveness."
 
[Ahmed 23583, 23595, Bukhari 144, 394, Muslim 264, Abu Dawud 9, Nisai 21, 22, Ibn e
Majah 318]