Abu Ali Suwaid bin Muqarrin (May Allah be pleased with him) said:
I was the seventh child of Banu Muqarrin and we had only one slave-girl. When the youngest of us once happened to slap her (on the face) the Messenger of Allah (ﷺ) ordered us to set her free.[Muslim]. (DE)
App reference (DE): Book 18, Hadith 93 (DE)
Arabic/English book reference (DE): Book 18, Hadith 1603 (DE)