Hadith
حَدَّثَنَا هِشَامُ بْنُ عَمَّارٍ، حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ أَبِي الرِّجَالِ، عَنْ أَبِيهِ، عَنْ عَمْرَةَ، عَنْ عَائِشَةَ، قَالَتْ أَقْسَمَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ أَنْ لاَ يَدْخُلَ عَلَى نِسَائِهِ شَهْرًا فَمَكَثَ تِسْعَةً وَعِشْرِينَ يَوْمًا حَتَّى إِذَا كَانَ مَسَاءَ ثَلاَثِينَ دَخَلَ عَلَىَّ فَقُلْتُ إِنَّكَ أَقْسَمْتَ أَنْ لاَ تَدْخُلَ عَلَيْنَا شَهْرًا . فَقَالَ " شَهْرٌ هَكَذَا " . يُرْسِلُ أَصَابِعَهُ فِيهَا ثَلاَثَ مَرَّاتٍ " وَشَهْرٌ هَكَذَا " . وَأَرْسَلَ أَصَابِعَهُ كُلَّهَا وَأَمْسَكَ إِصْبَعًا وَاحِدًا فِي الثَّالِثَةِ .
It was narrated that 'Aishah said:"The Messenger of Allah (ﷺ) swore that he would not enter upon his wives for a month, and he stayed for twenty-nine days until, on the eve of the thirtieth, he entered upon me. I said: 'You swore not to enter upon us for a month.' He said: 'The month may be like this,' and he held up his (ten) fingers three times; 'or the month may be like this,' and he held up his fingers three times, keeping one finger down on the third time
Sahih · Al-Albani
Sunan Ibn Majah 2059 ·Book 10, Hadith 44·Also available on sunnah.com·