Qatadah reported 'Umar b. al-Khattab (ra) as saying:If anyone gets possession of a relative who is within the prohibited degrees, that person becomes free.
حَدَّثَنَا مُحَمَّدُ بْنُ سُلَيْمَانَ، حَدَّثَنَا عَبْدُ الْوَهَّابِ، عَنْ سَعِيدٍ، عَنْ قَتَادَةَ، عَنِ الْحَسَنِ، قَالَ مَنْ مَلَكَ ذَا رَحِمٍ مَحْرَمٍ فَهُوَ حُرٌّ .
AbuDaud
The Book of Manumission of Slaves • Hadith 3951