عَنْ عَائِشَةَ رَضِيَ اَللَّهُ عَنْهَا
قَالَتْ: «آلَى رَسُولُ اَللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: مِنْ نِسَائِهِ وَحَرَّمَ، فَجَعَلَ اَلْحَرَامَ حَلَالًا، وَجَعَلَ لِلْيَمِينِ كَفَّارَةً»
The Messenger of Allah (sallallahu alayhi wa sallam) swore that he would stay away from his wives for a period. He made something unlawful (for himself) (i.e. something not in itself unlawful). So, he made the lawful unlawful, and he made atonement for breaking an oath.
Bulugh al-Maram 1266, Book 8, Marriage, Hadith 144. 1 min read