Sahih Muslim
The Book of Games and the Animals which May be Slaughtered and the Aninals that Are to be Eaten (Kitab-us-Said wal-Dhabaih wa ma Yukalu min Al-Hayawan)
Book Number: 021 / Hadith Number: 4771
Al-Bara' said: We found on the Day of Khaibar domestic asses, and the announcer of the Messenger of Allah (may peace be upon him) made an announcement that the earthen pots should be turned over.