SAHIH BUKHARI

Volume 1, Book 4, Number 150:

Narrated 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).