The Prophet ﷺ said, "Any slave who marries without his master's permission is a fornicator."
حدثنا علي بن حجر أخبرنا الوليد بن مسلم عن زهير بن محمد عن عبد الله بن محمد بن عقيل
عن النبي ﷺ قال أيما عبد تزوج بغير إذن سيده فهو عاهر
Its chain is daif. Abu Dawud narrated it in the Book of Marriage, chapter on the marriage of a slave without the permission of his masters, hadith 2078, from the hadith of Ibn Aqeel with this wording, and Hakim graded it sahih at 2/194, and Dhahabi agreed with him. There is also a narration on this subject from Ibn Umar [Abu Dawud, hadith 2079]. Ibn Aqeel, mentioned previously.