Sunan an-Nasa'i 37
سنن النسائي#37Sahihأَخْبَرَنَا مَحْمُودُ بْنُ غَيْلاَنَ، حَدَّثَنَا زَيْدُ بْنُ الْحُبَابِ، وَقَبِيصَةُ، قَالاَ أَنْبَأَنَا سُفْيَانُ، عَنِ الضَّحَّاكِ بْنِ عُثْمَانَ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، قَالَ مَرَّ رَجُلٌ عَلَى النَّبِيِّ صلى الله عليه وسلم وَهُوَ يَبُولُ فَسَلَّمَ عَلَيْهِ فَلَمْ يَرُدَّ عَلَيْهِ السَّلاَمَ .
It was narrated that Ibn 'Umar said:"A man passed by the Prophet (ﷺ) when he was urinating and greeted him with Salam, but he did not return his greeting
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:
Abu GhuddahHasan Sahih
Al-AlbaniHasan Sahih
Zubair Ali ZaiSahih Muslim
In-book reference: 1:37