Sahih Bukhari
Sahih Bukhari Volume 001, Book 004, Hadith Number 150.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 04. Ablutions (Wudu')
Narated By 'Abdullah bin 'Umar : I went up to the roof of Hafsa's house for some job and I saw Allah's Apostle answering the call of nature facing Sham (Syria, Jordan, Palestine and Lebanon regarded as one country) with his back towards the Qibla. (See Hadith No. 147).