وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ عَنِ الزُّبَيْرِ بْنِ الْعَوَّامِ، مِثْلُ ذَلِكَ ‏.‏ قَالَ مَالِكٌ فِي الأَمَةِ تَكُونُ عِنْدَ الرَّجُلِ فَيُصِيبُهَا ثُمَّ يُرِيدُ أَنْ يُصِيبَ أُخْتَهَا إِنَّهَا لاَ تَحِلُّ لَهُ حَتَّى يُحَرِّمَ عَلَيْهِ فَرْجَ أُخْتِهَا بِنِكَاحٍ أَوْ عِتَاقَةٍ أَوْ كِتَابَةٍ أَوْ مَا أَشْبَهَ ذَلِكَ يُزَوِّجُهَا عَبْدَهُ أَوْ غَيْرَ عَبْدِهِ ‏.‏

Yahya related to me from Malik that he had heard that az-Zubayribn al-Awwam said the like of that. Malik said that if a manhad sexual relations with a female slave that he owned, and then hewanted to also have relations with her sister, the sister was nothalal for a man until intercourse with the slave-girl had been madeharam for him by marriage, setting free, kitaba, or the like of that -for instance, if he had married her to his slave or someone other thanhis slave. Translation Not Available

Book reference: Muwatta Imam Malik Book 28 Hadith 1129
Web reference: Muwatta Imam Malik Book 28 Hadith 35