Sahih al-Bukhari 2001
صحيح البخاري#2001Sahihحَدَّثَنَا أَبُو الْيَمَانِ، أَخْبَرَنَا شُعَيْبٌ، عَنِ الزُّهْرِيِّ، قَالَ أَخْبَرَنِي عُرْوَةُ بْنُ الزُّبَيْرِ، أَنَّ عَائِشَةَ ـ رضى الله عنها ـ قَالَتْ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم أَمَرَ بِصِيَامِ يَوْمِ عَاشُورَاءَ، فَلَمَّا فُرِضَ رَمَضَانُ كَانَ مَنْ شَاءَ صَامَ، وَمَنْ شَاءَ أَفْطَرَ.
Narrated `Aisha:Allah's Messenger (ﷺ) ordered (the Muslims) to fast on the day of 'Ashura', and when fasting in the month of Ramadan was prescribed, it became optional for one to fast on that day ('Ashura') or not
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: 30:106