Khawlah was the wife of Aws ibn as-Samit; he was a man immensely given to sexual intercourse. When his desire for intercourse was intensified, he made his wife like his mother's back. So Allah, the Exalted, sent down Qur'anic verses relating to expiation for zihar. (Using translation from Abū Dāʾūd 2219)
«أَنَّ جَمِيلَةَ كَانَتِ امْرَأَةَ أَوْسِ بْنِ الصَّامِتِ وَكَانَ أَوْسٌ امْرَءًا بِهِ لَمَمٌ فَإِذَا اشْتَدَّ لَمَمُهُ ظَاهَرَ مِنَ امْرَأَتِهِ فَأَنْزَلَ اللَّهُ فِيهِ كَفَّارَةَ الظِّهَارِ»