When twenty-nine nights were over, which I had counted, the Messenger of Allah ﷺ came to me (he came to me first of all). I said: Messenger of Allah, you had taken an oath that you would not come to us for a month, whereas you have come after twenty nine days which I have counted. Whereupon he said: The month may also consist of twenty-nine days.  

أَنَّ النَّبِيَّ ﷺ أَقْسَمَ أَنْ لاَ يَدْخُلَ عَلَى أَزْوَاجِهِ شَهْرًا قَالَ الزُّهْرِيُّ فَأَخْبَرَنِي عُرْوَةُ عَنْ عَائِشَةَ ؓ قَالَتْ لَمَّا مَضَتْ تِسْعٌ وَعِشْرُونَ لَيْلَةً أَعُدُّهُنَّ دَخَلَ عَلَىَّ رَسُولُ اللَّهِ ﷺ قَالَتْ بَدَأَ بِي فَقُلْتُ يَا رَسُولَ اللَّهِ إِنَّكَ أَقْسَمْتَ أَنْ لاَ تَدْخُلَ عَلَيْنَا شَهْرًا وَإِنَّكَ دَخَلْتَ مِنْ تِسْعٍ وَعِشْرِينَ أَعُدُّهُنَّ فَقَالَ إِنَّ الشَّهْرَ تِسْعٌ وَعِشْرُونَ