Sahih Muslim 1084 b
Abu Zubair is reported to have heard Jabir b. 'Abdullah (Allah be pleased with both of them) as saying:
The Apostle of Allah (ﷺ) separated himself from his wives for a month. (His wives said: ) He came to us on the morning of the twenty-ninth. Upon this some, of the people said: It is the morning of twenty- ninth (according to our calculation). Upon this the Messenger of Allah (ﷺ) said: The month. may also consist of twenty-nine days. The Apostle of Allah (ﷺ) then flapped his bands thrice, twice with all the fingers of both his hand (to indicate twenty-nine) and by the third time with nine (fingers).
حَدَّثَنِي هَارُونُ بْنُ عَبْدِ اللَّهِ، وَحَجَّاجُ بْنُ الشَّاعِرِ، قَالاَ حَدَّثَنَا حَجَّاجُ بْنُ مُحَمَّدٍ، قَالَ قَالَ ابْنُ جُرَيْجٍ أَخْبَرَنِي أَبُو الزُّبَيْرِ، أَنَّهُ سَمِعَ جَابِرَ بْنَ عَبْدِ اللَّهِ، - رضى الله عنهما - يَقُولُ اعْتَزَلَ النَّبِيُّ صلى الله عليه وسلم نِسَاءَهُ شَهْرًا فَخَرَجَ إِلَيْنَا صَبَاحَ تِسْعٍ وَعِشْرِينَ فَقَالَ بَعْضُ الْقَوْمِ يَا رَسُولَ اللَّهِ إِنَّمَا أَصْبَحْنَا لِتِسْعٍ وَعِشْرِينَ ‏.‏ فَقَالَ النَّبِيُّ صلى الله عليه وسلم ‏
"‏ إِنَّ الشَّهْرَ يَكُونُ تِسْعًا وَعِشْرِينَ ‏"‏ ‏.‏ ثُمَّ طَبَّقَ النَّبِيُّ صلى الله عليه وسلم بِيَدَيْهِ ثَلاَثًا مَرَّتَيْنِ بِأَصَابِعِ يَدَيْهِ كُلِّهَا وَالثَّالِثَةَ بِتِسْعٍ مِنْهَا ‏.‏