Hadith #3999 (Sahih al-Bukhari)
Book: Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi)
Narrator(s): Zahir Al-Aslami
Grade: Sahih

(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.”

Source: https://parallelquran.com/hadith/sahih-al-bukhari-3999/