Hisham b. Urwa narrated it on the authority of his father:

Hakim b. Hizam freed one hundred slave and donated one hundred camels (for the sake of Allah) during the state of ignorance. Then he freed one hundred slaves and donated one hundred camel (for the sake of Allah) after) he had embraced Islam. He subsequently came to the Messenger (ﷺ). The rest of the hadith is the same as narrated above.

حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا عَبْدُ اللَّهِ بْنُ نُمَيْرٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، أَنَّ حَكِيمَ بْنَ حِزَامٍ، أَعْتَقَ فِي الْجَاهِلِيَّةِ مِائَةَ رَقَبَةٍ وَحَمَلَ عَلَى مِائَةِ بَعِيرٍ ثُمَّ أَعْتَقَ فِي الإِسْلاَمِ مِائَةَ رَقَبَةٍ وَحَمَلَ عَلَى مِائَةِ بَعِيرٍ ثُمَّ أَتَى النَّبِيَّ صلى الله عليه وسلم فَذَكَرَ نَحْوَ حَدِيثِهِمْ ‏.‏