'Abdullah bin 'Umar said:
"People say: 'When you sit to relieve yourself, do not face the Qiblah.' But one day I climbed up onto the roof of our house, and I saw the Messenger of Allah sitting on two bricks (to relieve himself), facing the direction of Baitul-Maqdis (Jerusalem)." This is a Hadith narrated by Yazid bin Harun. (DE)
English reference (DE): Vol. 1, Book 1, Hadith 322 (DE)
Arabic reference (DE): Book 1, Hadith 343 (DE)