Sayyiduna Ali (may Allah be pleased with him) said that a man asked him: he has two slave-women who are sisters; he has had intercourse with one and intends to have intercourse with the other? He said: It is not permissible until she leaves his ownership.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13938