Sunan an-Nasa'i, Hadith 2131 ⓘ
It was narrated that 'Aishah said: "The Messenger of Allah swore not to come to his wives for a month, and twenty-nine days passed. I said: 'Did you not wives to keep away from you wives for a month? I have counted twenty-nine days.' The Messenger of Allah said: 'The month is twenty-nine days."'
أَخْبَرَنَا نَصْرُ بْنُ عَلِيٍّ الْجَهْضَمِيُّ، عَنْ عَبْدِ الأَعْلَى، قَالَ حَدَّثَنَا مَعْمَرٌ، عَنِ الزُّهْرِيِّ، عَنْ عُرْوَةَ، عَنْ عَائِشَةَ، قَالَتْ أَقْسَمَ رَسُولُ اللَّهِ صلى الله عليه وسلم أَنْ لاَ يَدْخُلَ عَلَى نِسَائِهِ شَهْرًا فَلَبِثَ تِسْعًا وَعِشْرِينَ فَقُلْتُ أَلَيْسَ قَدْ كُنْتَ آلَيْتَ شَهْرًا فَعَدَدْتُ الأَيَّامَ تِسْعًا وَعِشْرِينَ . فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " الشَّهْرُ تِسْعٌ وَعِشْرُونَ " .
also referenced under: Book 22, Hadith 42 (In-Book) & Volume 3, Book 22, Hadith 2133 (DarusSalam)