Al-Hasan reported that a man ordered one of his slaves to draw water using one of his camels and the man fell asleep. The master came with a torch and put it in his face and the slave fell into the well. In the morning, the slave went to 'Umar ibn al-Khattab and 'Umar saw what had happened to his slave and therefore 'Umar set him free."
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا حَجَّاجُ بْنُ مِنْهَالٍ، قَالَ: حَدَّثَنَا حَمَّادُ بْنُ سَلَمَةَ، عَنْ عَلِيِّ بْنِ زَيْدٍ، عَنْ سَعِيدِ بْنِ الْمُسَيِّبِ، وَحَمَّادٍ، عَنْ حَبِيبٍ، وَحُمَيْدٍ، عَنِ الْحَسَنِ أَنَّ رَجُلاً أَمَرَ غُلاَمًا لَهُ أَنْ يَسْنُوَ عَلَى بَعِيرٍ لَهُ، فَنَامَ الْغُلاَمُ، فَجَاءَ بِشُعْلَةٍ مِنْ نَارٍ فَأَلْقَاهَا فِي وَجْهِهِ، فَتَرَدَّى الْغُلاَمُ فِي بِئْرٍ، فَلَمَّا أَصْبَحَ أَتَى عُمَرَ بْنَ الْخَطَّابِ رَضِيَ اللَّهُ عَنْهُ، فَرَأَى الَّذِي فِي وَجْهِهِ، فَأَعْتَقَهُ.
sunnah.com