Language:
كتاب النكاح
67  
Wedlock, Marriage (Nikaah)
(93)
Chapter: The decision of the Prophet (saws) not to share the beds with his wives and to stay away
(92)
باب هِجْرَةِ النَّبِيِّ صلى الله عليه وسلم نِسَاءَهُ فِي غَيْرِ بُيُوتِهِنَّ
Sahih al-Bukhari 5202

Narrated Um Salama:

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."

حَدَّثَنَا أَبُو عَاصِمٍ، عَنِ ابْنِ جُرَيْجٍ،‏.‏ وَحَدَّثَنِي مُحَمَّدُ بْنُ مُقَاتِلٍ، أَخْبَرَنَا عَبْدُ اللَّهِ، أَخْبَرَنَا ابْنُ جُرَيْجٍ، قَالَ أَخْبَرَنِي يَحْيَى بْنُ عَبْدِ اللَّهِ بْنِ صَيْفِيٍّ، أَنَّ عِكْرِمَةَ بْنَ عَبْدِ الرَّحْمَنِ بْنِ الْحَارِثِ، أَخْبَرَهُ أَنَّ أُمَّ سَلَمَةَ أَخْبَرَتْهُ أَنَّ النَّبِيَّ صلى الله عليه وسلم 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 ‏"‏‏.‏
Reference : Sahih al-Bukhari 5202
In-book reference : Book 67, Hadith 136
USC-MSA web (English) reference : Vol. 7, Book 62, Hadith 130
  (deprecated numbering scheme)