قَالَ مَالِكٌ فِي الْأَمَةِ تَكُونُ عِنْدَ الرَّجُلِ فَيُصِيبُهَا، ثُمَّ يُرِيدُ أَنْ يُصِيبَ أُخْتَهَا : إِنَّهَا لَا تَحِلُّ لَهُ حَتَّى يُحَرِّمَ عَلَيْهِ فَرْجَ أُخْتِهَا، بِنِكَاحٍ، أَوْ عِتَاقَةٍ، أَوْ كِتَابَةٍ، أَوْ مَا أَشْبَهَ ذَلِكَ، يُزَوِّجُهَا عَبْدَهُ أَوْ غَيْرَ
Imam Malik, may Allah have mercy on him, said: If a person has a slave woman and he has intercourse with her, then he wishes to have intercourse with her sister, this is not permissible. Until the private part of the first sister becomes forbidden for him, for example, he marries her off or gives her in marriage to his slave.