Maliks Muwatta Book 31, Hadith Number 66.

Yahya related to me from Malik from Abu’z-Zinad that Said ibn al-Musayyab said, “Bartering live animals for dead meat is forbidden.” Abu’z-Zinad said, “I said to Said ibn Musayyab, ‘What do you think of a man buying an old camel for 10 sheep?'” Said said, “If he buys it to slaughter it, there is no good in it.” Abu’z-Zinad added, “All the people (i.e. companions) that I have seen forbade bartering live animals for meat.”

Abu’z-Zinad said, “This used to be written in the appointment letters of governors in the time of Aban ibn Uthman and Hisham ibn Ismail.”