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 Apostle, 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.