The Prophet ﷺ said: If any slave marries without the permission of his masters, he is a fornicator. (Using translation from Abū Dāʾūd 2078)

قَالَ رَسُولُ اللهِ ﷺ أَيُّمَا عَبْدٍ تَزَوَّجَ بِغَيْرِ إِذْنِ مَوَالِيهِ أَوْ أَهْلِهِ فَهُوَ عَاهِرٌ