Ibn Tawus (may Allah have mercy on him) narrates from his father (may Allah have mercy on him) that it is not permissible for a free man to marry a slave woman when he is able to pay the dowry of a free woman. I said: "(What if) he fears zina?" He said: "I do not know it to be permissible (for him)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13995