Sahih al-Bukhari 1910
صحيح البخاري#1910Sahihحَدَّثَنَا أَبُو عَاصِمٍ، عَنِ ابْنِ جُرَيْجٍ، عَنْ يَحْيَى بْنِ عَبْدِ اللَّهِ بْنِ صَيْفِيٍّ، عَنْ عِكْرِمَةَ بْنِ عَبْدِ الرَّحْمَنِ، عَنْ أُمِّ سَلَمَةَ ـ رضى الله عنها ـ أَنَّ النَّبِيَّ صلى الله عليه وسلم آلَى مِنْ نِسَائِهِ شَهْرًا، فَلَمَّا مَضَى تِسْعَةٌ وَعِشْرُونَ يَوْمًا غَدَا أَوْ رَاحَ فَقِيلَ لَهُ إِنَّكَ حَلَفْتَ أَنْ لاَ تَدْخُلَ شَهْرًا. فَقَالَ " إِنَّ الشَّهْرَ يَكُونُ تِسْعَةً وَعِشْرِينَ يَوْمًا ".
Narrated Um Salama:The Prophet (ﷺ) vowed to keep aloof from his wives for a period of one month, and after the completion of 29 days he went either in the morning or in the afternoon to his wives. Someone said to him "You vowed that you would not go to your wives for one month." He replied, "The month is of 29 days
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 30:20