Maliks Muwatta Book 40, Hadith Number 8.
Malik said in the case of an umm walad who injured someone, “The blood-money of that injury is the responsibility of her master from his property, unless the blood-money of the injury is greater than the value of the umm walad. Her master does not have to pay more than her value. That is because when the master of a slave or slave-girl surrenders his slave or slave-girl for an injury which one of them has done, he does not owe any more than that, even if the blood-money is greater. As the master of the umm walad cannot surrender her because of the precedent of the sunna, when he pays her price, it is as if he had surrendered her. He does not have to pay more than that. This is the best of what I have heard about the matter. The master is not obliged to assume responsibility for more than an umm walad’s value because of her criminal action.”