Sunan an-Nasa'i 69
سنن النسائي#69Sahihأَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ بْنِ يَزِيدَ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنْ أَيُّوبَ، عَنْ مُحَمَّدٍ، عَنْ أَنَسٍ، قَالَ أَتَانَا مُنَادِي رَسُولِ اللَّهِ صلى الله عليه وسلم فَقَالَ إِنَّ اللَّهَ وَرَسُولَهُ يَنْهَاكُمْ عَنْ لُحُومِ الْحُمُرِ فَإِنَّهَا رِجْسٌ .
It was narrated that Anas said:"An announcer came to us from the Messenger of Allah (ﷺ) and said: 'Allah and His Messenger forbid you from (eating) the flesh of domestic donkeys, for it is filth
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 GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiSahih - Agreed Upon
In-book reference: 1:69