Sahih al-Bukhari 612
صحيح البخاري#612Sahihحَدَّثَنَا مُعَاذُ بْنُ فَضَالَةَ، قَالَ حَدَّثَنَا هِشَامٌ، عَنْ يَحْيَى، عَنْ مُحَمَّدِ بْنِ إِبْرَاهِيمَ بْنِ الْحَارِثِ، قَالَ حَدَّثَنِي عِيسَى بْنُ طَلْحَةَ، أَنَّهُ سَمِعَ مُعَاوِيَةَ، يَوْمًا فَقَالَ مِثْلَهُ إِلَى قَوْلِهِ " وَأَشْهَدُ أَنَّ مُحَمَّدًا رَسُولُ اللَّهِ ".
Narrated `Isa bin Talha:that he had heard Muawiya repeating the words of Adhan up to "Wa ash-hadu anna Muhammadan rasulul-lah (and I testify that Muhammad is Allah's Messenger (ﷺ)
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: 10:10