The Prophet ﷺ took an oath that he would not enter upon some of his wives for one month. But when twenty nine days had elapsed, he went to them in the morning or evening. It was said to him, "O Allah's Prophet! You had taken an oath that you would not enter upon them for one month." He replied, "The month can be of twenty nine days." (Using translation from Bukhārī 5202)   

أَنَّ النَّبِيَّ ﷺ «حَلَفَ أَنْ لَا يَدْخُلُ عَلَى بَعْضِ أَهْلِهِ شَهْرًا فَلَمَّا مَضَتْ تِسْعٌ وَعِشْرُونَ لَيْلَةً غَدَا عَلَيْهِنَّ» فَقِيلَ لَهُ إِنَّكَ حَلَفْتَ أَنْ لَا تَدْخُلَ عَلَيْهِنَّ شَهْرًا قَالَ «إِنَّ الشَّهْرَ يَكُونُ تِسْعَةً وَعِشْرِينَ يَوْمًا»  

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). (Using translation from Muslim 1084b)   

أَنَّهُ سَمِعَ جَابِرًا يَقُولُ اعْتَزَلَ رَسُولُ اللهِ ﷺ نِسَاءَهُ شَهْرًا فَخَرَجَ صَبَاحَ تِسْعَةٍ وَعِشْرِينَ فَقَالَ النَّبِيُّ ﷺ «إِنَّ الشَّهْرَ يَكُونُ تِسْعَةً وَعِشْرِينَ» ثُمَّ صَفَّقَ نَبِيُّ اللهِ ﷺ بِيَدَيْهِ ثَلَاثًا مَرَّتَيْنِ بِأَصَابِعِ يَدَيْهِ كُلِّهَا وَالثَّالِثَةَ بِالتِّسْعِ مِنْهَا