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bukhari:4087ʿAbdullāh b. Muḥammad > Sufyān > ʿAmr > Jābir

The person who killed Khubaib was Abu Sarua (i.e. ʿUqba bin Al-Harith).  

البخاري:٤٠٨٧حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مُحَمَّدٍ حَدَّثَنَا سُفْيَانُ عَنْ عَمْرٍو

سَمِعَ جَابِرًا يَقُولُ الَّذِي قَتَلَ خُبَيْبًا هُوَ أَبُو سِرْوَعَةَ