Amir, Masruq and Ibrahim al-Nakha'i narrated from Sayyiduna Ibn Mas'ud (may Allah be pleased with him) that he used to say: "The master's intercourse with a slave girl does not make her lawful for her (former) husband, until she marries another husband."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9673