Sahih Bukhari
Ablutions (Wudu)
Volume: 001 / Book Number: 004 / Hadith Number: 151
Narrated 'Abdullah bin 'Umar:
Once I went up the roof of our house and saw Allah's Apostle answering the call of nature while sitting over two bricks facing Bait-ul-Maqdis (Jerusalem). (See Hadith No. 147).