Malik said, "A master who frees a slave of his and settles hisemancipation so that his testimony is permitted, his inviolabilitycomplete, and his right to inherit confirmed, cannot imposestipulations on him like what he imposes on a slave about property orservice, nor get him to do anything of slavery, because the Messengerof Allah, may Allah bless him and grant him peace, said, "If a manfrees his share of a slave and has enough money to cover the fullprice of the slave justly evaluated for him, he must give his partnerstheir shares so the slave is completely free."Malikcommented, "If he owns the slave completely, it is more proper to freehim completely and not mingle any slavery with it."
USC-MSA web (English) reference: Book 38, Hadith 2