Sunan Abi Dawud, Hadith 3951

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 ‏.‏

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also referenced under: Hadith 3940 (Hasan)