It was narrated that 'Aishah said:

"The Messenger of Allah swore to keep away from his wives and declared them as unlawful for him, so he made something permissible forbidden, and he offered expiation for having sworn to do so."

حَدَّثَنَا الْحَسَنُ بْنُ قَزَعَةَ، حَدَّثَنَا مَسْلَمَةُ بْنُ عَلْقَمَةَ، حَدَّثَنَا دَاوُدُ بْنُ أَبِي هِنْدٍ، عَنْ عَامِرٍ، عَنْ مَسْرُوقٍ، عَنْ عَائِشَةَ، قَالَتْ آلَى رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ مِنْ نِسَائِهِ وَحَرَّمَ فَجَعَلَ الْحَرَامَ حَلاَلاً ‏.‏ وَجَعَلَ فِي الْيَمِينِ كَفَّارَةً ‏.‏