Sahih al-Bukhari 41
صحيح البخاري#41Sahihقَالَ مَالِكٌ أَخْبَرَنِي زَيْدُ بْنُ أَسْلَمَ، أَنَّ عَطَاءَ بْنَ يَسَارٍ، أَخْبَرَهُ أَنَّ أَبَا سَعِيدٍ الْخُدْرِيَّ أَخْبَرَهُ أَنَّهُ، سَمِعَ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ " إِذَا أَسْلَمَ الْعَبْدُ فَحَسُنَ إِسْلاَمُهُ يُكَفِّرُ اللَّهُ عَنْهُ كُلَّ سَيِّئَةٍ كَانَ زَلَفَهَا، وَكَانَ بَعْدَ ذَلِكَ الْقِصَاصُ، الْحَسَنَةُ بِعَشْرِ أَمْثَالِهَا إِلَى سَبْعِمِائَةِ ضِعْفٍ، وَالسَّيِّئَةُ بِمِثْلِهَا إِلاَّ أَنْ يَتَجَاوَزَ اللَّهُ عَنْهَا ".
Narrated Abu Sa'id Al Khudri:Allah's Messenger (ﷺ) said, "If a person embraces Islam sincerely, then Allah shall forgive all his past sins, and after that starts the settlement of accounts, the reward of his good deeds will be ten times to seven hundred times for each good deed and one evil deed will be recorded as it is unless Allah forgives it
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: 2:34