بُلُوغُ الْمَرَامِ
Bulugh al-Maram 1088
Marriage
عَنْ عَائِشَةَ رَضِيَ اَللَّهُ عَنْهَا قَالَتْ: { آلَى رَسُولُ اَللَّهِ - صلى الله عليه وسلم -مِنْ نِسَائِهِ وَحَرَّمَ, فَجَعَلَ اَلْحَرَامَ حَلَالًا , وَجَعَلَ لِلْيَمِينِ كَفَّارَةً. } رَوَاهُ اَلتِّرْمِذِيُّ, وَرُوَاتُهُ ثِقَاتٌ . [1] .
Narrated 'Aishah (RA): Allah's Messenger (ﷺ) 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. [Reported by at-Tirmidhi, and its narrators are reliable (thiqah)].
Sunnah.com reference: Book 8, Hadith 144