You could find no other part (to slap) but the prominent part of her face. See I was one of the seven sons of Muqarrin, and we had but only one slave-girl. The youngest of us slapped her, and Messenger of Allah ﷺ commanded us to set her free. 2097  

لَهُ سُوَيْدُ بْنُ مُقَرِّنٍ عَجَزَ عَلَيْكَ إِلاَّ حُرُّ وَجْهِهَا لَقَدْ رَأَيْتُنِي سَابِعَ سَبْعَةٍ مِنْ بَنِي مُقَرِّنٍ مَا لَنَا خَادِمٌ إِلاَّ وَاحِدَةٌ لَطَمَهَا أَصْغَرُنَا فَأَمَرَنَا رَسُولُ اللَّهِ ﷺ أَنْ نُعْتِقَهَا  

We were staying in the house of Suwaid b. Muqarrin. There was among us an old man who was hot-tempered. He had a slave-girl with him. He gave a slap on her face. I never saw Suwaid more angry than on that day. He said: there is no alternative for you except to free her. I was the seventh child in order of Muqarrin and we had only a female servant. The youngest of us gave a slap on her face. The prophet (May peace be upon him) commanded us to set her free.  

عَجَزَ عَلَيْكَ إِلاَّ حُرُّ وَجْهِهَا لَقَدْ رَأَيْتُنَا سَابِعَ سَبْعَةٍ مِنْ وَلَدِ مُقَرِّنٍ وَمَا لَنَا إِلاَّ خَادِمٌ فَلَطَمَ أَصْغَرُنَا وَجْهَهَا فَأَمَرَنَا النَّبِيُّ ﷺ بِعِتْقِهَا  

[Machine] Did you find anything except a free face? I have seen myself, and we are the seventh of seven sons of Muqarrin. We have only one servant whom one of us has appointed, and he slapped him. Then the Messenger of Allah ﷺ commanded us that when we return, we should set him free, so we set him free.  

أَمَا وَجَدْتَ إِلَّا حُرَّ وَجْهِهِ وَلَقَدْ رَأَيْتُنِي وَنَحْنُ سَابِعُ سَبْعَةٍ مِنْ وَلَدِ مُقَرِّنٍ وَمَا لَنَا خَادِمٌ إِلَّا وَاحِدٌ عَمَدَ إِلَيْهِ وَاحِدٌ فَلَطَمَهُ فَأَمَرَنَا رَسُولُ اللهِ ﷺ إِذَا رَجَعْنَا أَنْ نُعْتِقَهُ فَأَعْتَقْنَاهُ  

[Machine] Walidah, a Swaidi woman, was slapped, which made her very angry. She had never been so angry before. She said, "May the curse of Allah be upon you, except for the sacredness of her face. I have seen myself as the seventh of seven from the Bani Muqarrin tribe. We have only one servant, and he slapped her, our youngest. The Messenger of Allah, peace be upon him, ordered us to set her free." It is authentic.  

وَلِيدَةُ سُوَيْدٍ فَلَطَمَهَا فَغَضِبَ مِنْ ذَلِكَ غَضَبًا مَا غَضِبَ مِثْلَهُ قَطُّ قَالَ «عَجَزَ عَلَيْكَ إِلَّا حُرُّ وَجْهِهَا لَقَدْ رَأَيْتُنِي سَابِعَ سَبْعَةٍ مِنْ بَنِي مُقَرِّنٍ مَا لَنَا إِلَّا خَادِمٌ وَاحِدٌ فَلَطَمَهَا أَصْغَرُنَا فَأَمَرَنَا رَسُولُ اللَّهِ ﷺ أَنْ نُعْتِقَهَا» صحيح  

[Machine] "You slapped her face. I saw myself as the seventh of seven. We have nothing except a servant. So a man slapped her. The Messenger of Allah ﷺ then ordered us to set him free."  

«لَطَمْتَ وَجْهَهَا لَقَدْ رَأَيْتُنِي سَابِعَ سَبْعَةٍ مَا لَنَا إِلَّا خَادِمٌ فَلَطَمَهُ رَجُلٌ فَأَمَرَنَا رَسُولُ اللهِ ﷺ أَنْ نَعْتِقَهُ»