The Prophet (ﷺ) reached Khaibar in the morning, while the people were coming out carrying their spades
over their shoulders. When they saw him they said, "This is Muhammad and his army! Muhammad
and his army!" So, they took refuge in the fort. The Prophet (ﷺ) raised both his hands and said, "Allahu
Akbar, Khaibar is ruined, for when we approach a nation (i.e. enemy to fight) then miserable is the
morning of the warned ones." Then we found some donkeys which we (killed and) cooked: The
announcer of the Prophet (ﷺ) announced: "Allah and His Apostle forbid you to eat donkey's meat." So, all
the pots including their contents were turned upside down.
Sahih al-Bukhari Book 56, Hadith 200