From Sahih Bukhari (Hadith 148):
Narrated `Abdullah bin `Umar:I went up to the roof of Hafsa's house for some job and I saw Allah's Messenger (ﷺ) 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)
Reference: Bukhari 148