Sahih al-Bukhari 5102
صحيح البخاري#5102Sahihحَدَّثَنَا أَبُو الْوَلِيدِ، حَدَّثَنَا شُعْبَةُ، عَنِ الأَشْعَثِ، عَنْ أَبِيهِ، عَنْ مَسْرُوقٍ، عَنْ عَائِشَةَ ـ رضى الله عنها ـ أَنَّ النَّبِيَّ صلى الله عليه وسلم دَخَلَ عَلَيْهَا وَعِنْدَهَا رَجُلٌ، فَكَأَنَّهُ تَغَيَّرَ وَجْهُهُ، كَأَنَّهُ كَرِهَ ذَلِكَ فَقَالَتْ إِنَّهُ أَخِي. فَقَالَ " انْظُرْنَ مَا إِخْوَانُكُنَّ، فَإِنَّمَا الرَّضَاعَةُ مِنَ الْمَجَاعَةِ ".
Narrated `Aisha:that the Prophet (ﷺ) entered upon her while a man was sitting with her. Signs of answer seemed to appear on his face as if he disliked that. She said, "Here is my (foster) brother." He said, "Be sure as to who is your foster brother, for foster suckling relationship is established only when milk is the only food of the child
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: 67:40