Muhammad bin Ja'far narrated to us, from Shu'bah, from Amr bin Murrah who said: "I asked Abu Ubaidah bin Abdullah: 'Did you remember anything from Abdullah?' He said, 'No'" (Using translation from Tirmidhī 624)   

أَنَّهُ بَلَغَهُ أَنَّ عَبْدَ اللهِ بْنَ عُمَرَ سُئِلَ عَنِ الرَّقَبَةِ الْوَاجِبَةِ فَقِيلَ لَهُ هَلْ تُشْتَرَى بِشَرْطٍ قَالَ لَا