Sahih al-Bukhari 144
صحيح البخاري#144SahihNarrated 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
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 4:10