Sunan an-Nasa'i · Book 1 · Hadith 69
أَخْبَرَنَا 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.'"
Sahih