Narrated Zahir Al-Aslami:(who was one of those who had witnessed (the Pledge of allegiance beneath) the Tree) While I was making fire beneath the cooking pots containing donkey's meat, the announcer of Allah's Messenger (ﷺ) announced, "Allah's Messenger (ﷺ) forbids you to eat donkey's meat."
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مُحَمَّدٍ، حَدَّثَنَا أَبُو عَامِرٍ، حَدَّثَنَا إِسْرَائِيلُ، عَنْ مَجْزَأَةَ بْنِ زَاهِرٍ الأَسْلَمِيِّ، عَنْ أَبِيهِ ـ وَكَانَ مِمَّنْ شَهِدَ الشَّجَرَةَ ـ قَالَ إِنِّي لأُوقِدُ تَحْتَ الْقِدْرِ بِلُحُومِ الْحُمُرِ إِذْ نَادَى مُنَادِي رَسُولِ اللَّهِ صلى الله عليه وسلم إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم يَنْهَاكُمْ عَنْ لُحُومِ الْحُمُرِ.
Bukhari
Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi) • Hadith 215