Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) used to say: When a slave marries without the permission of his master, the divorce is in the slave's hands. It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) concerning a slave who married a free woman without his master's permission: She is a woman who has made her private part lawful.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13733