The rule for one who finds his father enslaved in the pre-Islamic era

سَأَلْتُ أَبَا عَبْدِ اللَّهِ ع- عَنْ رَجُلٍ أَصَابَ أَبَاهُ سَبْيٌ فِي الْجَاهِلِيَّةِ فَلَمْ يَعْلَمْ أَنَّهُ كَانَ أَصَابَ أَبَاهُ سَبْيٌ فِي الْجَاهِلِيَّةِ إِلَّا بَعْدَ مَا تَوَالَدَتْهُ الْعَبِيدُ فِي الْإِسْلَامِ وَ أُعْتِقَ قَالَ فَقَالَ فَلْيُنْسَبْ إِلَى آبَائِهِ الْعَبِيدِ فِي الْإِسْلَامِ ثُمَّ هُوَ يُعَدُّ مِنَ الْقَبِيلَةِ الَّتِي كَانَ أَبُوهُ سُبِيَ فِيهَا إِنْ كَانَ [أَبُوهُ‌] مَعْرُوفاً فِيهِمْ وَ

‘His lineage is to his enslaved father in Al-Islam, then he would be counted from the tribe which his father was enslaved in, that he was known to be from them, and he will inherit from them and they will inherit from him’.