Sunan an-Nasa'i 21
سنن النسائي#21Sahihأَخْبَرَنَا مُحَمَّدُ بْنُ مَنْصُورٍ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنِ الزُّهْرِيِّ، عَنْ عَطَاءِ بْنِ يَزِيدَ، عَنْ أَبِي أَيُّوبَ، أَنَّ النَّبِيَّ صلى الله عليه وسلم قَالَ " لاَ تَسْتَقْبِلُوا الْقِبْلَةَ وَلاَ تَسْتَدْبِرُوهَا لِغَائِطٍ أَوْ بَوْلٍ وَلَكِنْ شَرِّقُوا أَوْ غَرِّبُوا " .
It was narrated from Abu Ayyub that the Prophet (ﷺ) said:"Do not face towards the Qiblah nor turn your backs toward it when defecating or urinating, rather face toward the east or the west
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
In-book reference: 1:21