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Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
abudawud:4517 – al-Ḥasan b. ʿAlī > Saʿīd b. ʿĀmir > Ibn Abū ʿArūbah

Then al-Hasan forgot this tradition, and he used to say: A free man is not to be killed for a slave.  

أبو داود:٤٥١٧ – حَدَّثَنَا الْحَسَنُ بْنُ عَلِيٍّ حَدَّثَنَا سَعِيدُ بْنُ عَامِرٍ عَنِ ابْنِ أَبِي عَرُوبَةَ

عَنْ قَتَادَةَ بِإِسْنَادِ شُعْبَةَ مِثْلَهُ زَادَ ثُمَّ إِنَّ الْحَسَنَ نَسِيَ هَذَا الْحَدِيثَ فَكَانَ يَقُولُ لاَ يُقْتَلُ حُرٌّ بِعَبْدٍ