Mishkat al-Masabih
Mishkat al-Masabih 2373
وَعَنْ أَبِي سَعِيدٍ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: " إِذَا أَسْلَمَ الْعَبْدُ فَحَسُنَ إِسْلَامُهُ يُكَفِّرُ اللَّهُ عَنْهُ كُلَّ سَيِّئَةٍ كَانَ زَلَفَهَا وَكَانَ بَعْدَ الْقِصَاصِ: الْحَسَنَةُ بِعَشْرِ أَمْثَالِهَا إِلَى سَبْعِمِائَةِ ضِعْفٍ إِلَى أَضْعَافٍ كَثِيرَةٍ وَالسَّيِّئَةُ بِمِثْلِهَا إِلَّا أَنْ يَتَجَاوَزَ اللَّهُ عَنْهَا ". رَوَاهُ البُخَارِيّ
Abu Sa‘id reported that the Messenger of God (peace be upon him) said: ‘When a servant embraces Islam and makes his Islam good, God expiates every sin he committed before it. After requital, a good deed is multiplied tenfold, up to seven hundred times and many times more; an evil deed is counted as one like it, unless God pardons it.’ Al-Bukhari transmitted it. The Arabic source grades it sahih (al-Albani).