Sahih al-Bukhari 1170
صحيح البخاري#1170Sahihحَدَّثَنَا آدَمُ، قَالَ أَخْبَرَنَا شُعْبَةُ، أَخْبَرَنَا عَمْرُو بْنُ دِينَارٍ، قَالَ سَمِعْتُ جَابِرَ بْنَ عَبْدِ اللَّهِ ـ رضى الله عنهما ـ قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم وَهُوَ يَخْطُبُ " إِذَا جَاءَ أَحَدُكُمْ وَالإِمَامُ يَخْطُبُ ـ أَوْ قَدْ خَرَجَ ـ فَلْيُصَلِّ رَكْعَتَيْنِ ".
Narrated Jabir bin `Abdullah:While delivering a sermon, Allah's Messenger (ﷺ) said, "If anyone of you comes while the Imam is delivering the sermon or has come out for it, he should offer a two rak`at prayer
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: 19:49