Sahih al-Bukhari 4911Book 65, Hadith 431
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}.
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.