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.
In-book : Book 12, Hadith 34
English translation : Book 11, Hadith 2074
12. Marriage (Kitab Al-Nikah)
باب فِي نِكَاحِ الْعَبْدِ بِغَيْرِ إِذْنِ مَوَالِيهِ