وَحَدَّثَنَا أَبُو كُرَيْبٍ، مُحَمَّدُ بْنُ الْعَلاَءِ حَدَّثَنَا أَبُو مُعَاوِيَةَ، حَدَّثَنَا الأَعْمَشُ، عَنْ إِبْرَاهِيمَ، التَّيْمِيِّ عَنْ أَبِيهِ، عَنْ أَبِي مَسْعُودٍ الأَنْصَارِيِّ، قَالَ كُنْتُ أَضْرِبُ غُلاَمًا لِي فَسَمِعْتُ مِنْ خَلْفِي صَوْتًا ‏"‏ اعْلَمْ أَبَا مَسْعُودٍ لَلَّهُ أَقْدَرُ عَلَيْكَ مِنْكَ عَلَيْهِ ‏"‏ ‏.‏ فَالْتَفَتُّ فَإِذَا هُوَ رَسُولُ اللَّهِ صلى الله عليه وسلم فَقُلْتُ يَا رَسُولَ اللَّهِ هُوَ حُرٌّ لِوَجْهِ اللَّهِ ‏.‏ فَقَالَ ‏"‏ أَمَا لَوْ لَمْ تَفْعَلْ لَلَفَحَتْكَ النَّارُ أَوْ لَمَسَّتْكَ النَّارُ ‏"‏ ‏.‏

Abu Mas'ud al-Ansari reported: When I was beating my servant, I heard a voice behind me (saying): Abu Mas'ud, bear in mind Allah has more dominance over you than you have upon him. I turned and (found him) to be Allah's Messenger (PBUH). I said: Allah's Messenger, I set him free for the sake of Allah. Thereupon he said: Had you not done that, (the gates of) Hell would have opened for you, or the fire would have burnt you. Translation Not Available

Book Ref: Sahih Muslim Book 27 Hadith 4088
Web Ref:  Sahih Muslim Book 15 Hadith 1659 c