The Prophet ﷺ said: If any slave marries without the permission of his masters, he is a fornicator.  

قَالَ رَسُولُ اللَّهِ ﷺ أَيُّمَا عَبْدٍ تَزَوَّجَ بِغَيْرِ إِذْنِ مَوَالِيهِ فَهُوَ عَاهِرٌ  

Ibn ‘Umar reported the Prophet ﷺ as saying “If a slave marries without the permission of his master, his marriage is null and void. Abu Dawud said “This tradition is weak. This is mauquf(does not go back to the Prophet). This is the statement of the Ibn ‘Umar himself.  

أَنَّ النَّبِيَّ ﷺ قَالَ إِذَا نَكَحَ الْعَبْدُ بِغَيْرِ إِذْنِ مَوْلاَهُ فَنِكَاحُهُ بَاطِلٌ