حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، أَنَّهُ سَمِعَ رَبِيعَةَ بْنَ أَبِي عَبْدِ الرَّحْمَنِ، يَقُولُ يَنْكِحُ الْعَبْدُ أَرْبَعَ نِسْوَةٍ ‏.‏ قَالَ مَالِكٌ وَهَذَا أَحْسَنُ مَا سَمِعْتُ فِي ذَلِكَ ‏.‏ قَالَ مَالِكٌ وَالْعَبْدُ مُخَالِفٌ لِلْمُحَلِّلِ إِنْ أَذِنَ لَهُ سَيِّدُهُ ثَبَتَ نِكَاحُهُ وَإِنْ لَمْ يَأْذَنْ لَهُ سَيِّدُهُ فُرِّقَ بَيْنَهُمَا وَالْمُحَلِّلُ يُفَرَّقُ بَيْنَهُمَا عَلَى كُلِّ حَالٍ إِذَا أُرِيدَ بِالنِّكَاحِ التَّحْلِيلُ ‏.‏ قَالَ مَالِكٌ فِي الْعَبْدِ إِذَا مَلَكَتْهُ امْرَأَتُهُ أَوِ الزَّوْجُ يَمْلِكُ امْرَأَتَهُ إِنَّ مِلْكَ كُلِّ وَاحِدٍ مِنْهُمَا صَاحِبَهُ يَكُونُ فَسْخًا بِغَيْرِ طَلاَقٍ وَإِنْ تَرَاجَعَا بِنِكَاحٍ بَعْدُ لَمْ تَكُنْ تِلْكَ الْفُرْقَةُ طَلاَقًا ‏.‏ قَالَ مَالِكٌ وَالْعَبْدُ إِذَا أَعْتَقَتْهُ امْرَأَتُهُ إِذَا مَلَكَتْهُ وَهِيَ فِي عِدَّةٍ مِنْهُ لَمْ يَتَرَاجَعَا إِلاَّ بِنِكَاحٍ جَدِيدٍ ‏.‏

Yahya related to me from Malik that he heard Rabia ibn Abd ar-Rahman say that a slave could marry four women. Malik said,"This is the best of what I have heard about the matter." Malik said, "The slave differs with the muhallil if the slave is givenpermission by his master for his ex-wife. If his master does not givehim permission, he separates them. The muhallil is separated in anycase if he intends to make the woman halal by marriage." Malik said, "When a slave is owned by his wife or a husband owns hiswife, the possession of each of them is rendered void without divorce.If a man, for instance, is married to a slave-girl, and then he buysher, he must divorce her as a matter of course. They can then re-marry. If they re-marry afterwards, that separation was not divorce." Malik said, "When a slave is freed by his wife who owns himand she is in the idda-period from him, they can only return to eachother after she has made another marriage." Translation Not Available

Book Ref: Muwatta Imam Malik Book 28 Hadith 1138
Web Ref:  Muwatta Imam Malik Book 28 Hadith 43