Sahih Bukhari Volume 003, Book 043, Hadith Number 657.
Narated By Salama bin Al-Akwa : On the day of Khaibar the Prophet saw fires being lighted. He asked, "Why are these fires being lighted?" The people replied that they were cooking the meat of donkeys. He said, "Break the pots and throw away their contents." The people said, "Shall we throw away their contents and wash the pots (rather than break them)?" He said, "Wash them."