Sahih al-Bukhari, Book 65, Hadith 4911 (In-Book) ⓘ
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, 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}.
also referenced under: Hadith 4911 (DarusSalam) & Volume 6, Book 60, Hadith 433 (USC-MSA)