Sahih al-Bukhari 4911
Narrated Ibn `Abbas:
If someone says to his wife, "You are unlawful to me." he must make an expiation (for his oath). Ibn 
`Abbas added: There is for you in Allah's Messenger (ﷺ), an excellent example to follow.
حَدَّثَنَا مُعَاذُ بْنُ فَضَالَةَ، حَدَّثَنَا هِشَامٌ، عَنْ يَحْيَى، عَنِ ابْنِ حَكِيمٍ، عَنْ سَعِيدِ بْنِ جُبَيْرٍ، أَنَّ ابْنَ عَبَّاسٍ ـ رضى الله عنهما ـ قَالَ فِي الْحَرَامِ يُكَفِّرُ‏.‏ وَقَالَ ابْنُ عَبَّاسٍ ‏{‏لَقَدْ كَانَ لَكُمْ فِي رَسُولِ اللَّهِ إِسْوَةٌ حَسَنَةٌ‏}‏‏.‏