It was narrated from Salamah bin Muhabbiq that:

the case of a man who had intercourse with the slave woman of his wife was referred to the Messenger of Allah (ﷺ), and he did not stipulate any legal punishment for him.

حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا عَبْدُ السَّلاَمِ بْنُ حَرْبٍ، عَنْ هِشَامِ بْنِ حَسَّانَ، عَنِ الْحَسَنِ، عَنْ سَلَمَةَ بْنِ الْمُحَبِّقِ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم رُفِعَ إِلَيْهِ رَجُلٌ وَطِئَ جَارِيَةَ امْرَأَتِهِ فَلَمْ يَحُدَّهُ ‏.‏