(11) باب لاَ تُسْتَقْبَلُ الْقِبْلَةُ بِغَائِطٍ أَوْ بَوْلٍ إِلاَّ عِنْدَ الْبِنَاءِ جِدَارٍ أَوْ نَحْوِهِ
Narrated Abu Aiyub Al-Ansari:
Allah's Messenger (ﷺ) said, "If anyone of you goes to an open space for answering the call of nature he should neither face nor turn his back towards the Qibla; he should either face the east or the west."
Reference: Sahih al-Bukhari 144
In-book reference: Book 4, Hadith 10
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 4, Hadith 146