Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said that marrying a free woman while having a slave wife is the divorce of the slave woman.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 14007
Masruq (may Allah have mercy on him) said: It is like carrion, to which one is driven by necessity; when Allah makes you free of need for it, then you too should do without it and be independent of it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 14008
Masruq (may Allah have mercy on him) said: When you marry a free woman while having a slave wife, that is the divorce of the slave woman. It is like carrion, which is eaten in a time of necessity; when he no longer needs it, he should refrain.
We hold only what we have narrated on this from Sayyiduna Ali and Sayyiduna Jabir bin Abdullah (may Allah be pleased with them both), and success is from Allah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 14009