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."  

أَنَّ النَّبِيَّ ﷺ حَلَفَ لاَ يَدْخُلُ عَلَى بَعْضِ أَهْلِهِ شَهْرًا فَلَمَّا مَضَى تِسْعَةٌ وَعِشْرُونَ يَوْمًا غَدَا عَلَيْهِنَّ أَوْ رَاحَ فَقِيلَ لَهُ يَا نَبِيَّ اللَّهِ حَلَفْتَ أَنْ لاَ تَدْخُلَ عَلَيْهِنَّ شَهْرًا قَالَ إِنَّ الشَّهْرَ يَكُونُ تِسْعَةً وَعِشْرِينَ يَوْمًا  

One morning we saw the wives of the Prophet ﷺ weeping, and everyone of them had her family with her, I went to the mosque and found that it was crowded with people. Then ʿUmar bin Al-Khattab came and went up to the Prophet ﷺ who was in his upper room. He greeted him but nobody answered. He greeted again, but nobody answered. Then the gatekeeper called him and he entered upon the Prophet, and asked, "Have you divorced your wives?" The Prophet, said, "No, but I have taken an oath not to go to them for one month." So the Prophet ﷺ stayed away (from his wives) for twenty nine days and then entered upon them.  

أَصْبَحْنَا يَوْمًا وَنِسَاءُ النَّبِيِّ ﷺ يَبْكِينَ عِنْدَ كُلِّ امْرَأَةٍ مِنْهُنَّ أَهْلُهَا فَخَرَجْتُ إِلَى الْمَسْجِدِ فَإِذَا هُوَ مَلآنُ مِنَ النَّاسِ فَجَاءَ عُمَرُ بْنُ الْخَطَّابِ فَصَعِدَ إِلَى النَّبِيِّ ﷺ وَهْوَ فِي غُرْفَةٍ لَهُ فَسَلَّمَ فَلَمْ يُجِبْهُ أَحَدٌ ثُمَّ سَلَّمَ فَلَمْ يُجِبْهُ أَحَدٌ ثُمَّ سَلَّمَ فَلَمْ يُجِبْهُ أَحَدٌ فَنَادَاهُ فَدَخَلَ عَلَى النَّبِيِّ ﷺ فَقَالَ أَطَلَّقْتَ نِسَاءَكَ فَقَالَ لاَ وَلَكِنْ آلَيْتُ مِنْهُنَّ شَهْرًا فَمَكَثَ تِسْعًا وَعِشْرِينَ ثُمَّ دَخَلَ عَلَى نِسَائِهِ