عَنْ أُمِّ سَلَمَةَ رَضِيَ اللَّهُ عَنْهَا أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ حَلَفَ أَنْ لَا يَدْخُلَ عَلَى بَعْضِ أَهْلِهِ شَهْرًا فَلَمَّا مَضَى تِسْعَةٌ وَعِشْرُونَ يَوْمًا غَدَا عَلَيْهِمْ أَوْ رَاحَ فَقِيلَ لَهُ حَلَفْتَ يَا نَبِيَّ اللَّهِ لَا تَدْخُلُ عَلَيْهِنَّ شَهْرًا فَقَالَ إِنَّ الشَّهْرَ تِسْعَةٌ وَعِشْرُونَ يَوْمًا
It is narrated from Sayyida Umm Salama (may Allah be pleased with her) that the Noble Prophet (peace and blessings be upon him) took an oath not to go to some of his wives for a month. When twenty-nine days had passed, either in the morning or evening, the Prophet (peace and blessings be upon him) went to them. Someone asked him: O Messenger of Allah! Did you not swear not to enter upon them for a month? The Prophet (peace and blessings be upon him) replied: Indeed, this month is of twenty-nine days.