كتاب التوبة
50
The Book of Repentance
(8)
Chapter: The Acceptance Of The Repentance Of The One Who Kills, Even If He Has Killed A Great Deal
(8)
باب قَبُولِ تَوْبَةِ الْقَاتِلِ وَإِنْ كَثُرَ قَتْلُهُ ‏‏
Sahih Muslim 2767 d

Abu Burda reported Allah's Messenger (ﷺ) as saying:

There would come people amongst the Muslims on the Day of Resurrection with as heavy sins as a mountain, and Allah would forgive them and He would place in their stead the Jews and the Christians. (As far as I think), Abu Raub said: I do not know as to who is in doubt. Abu Burda said: I narrated it to 'Umar b. 'Abd al-'Aziz, whereupon he said: Was it your father who narrated it to you from Allah's Apostle (ﷺ)? I said: Yes.
حَدَّثَنَا مُحَمَّدُ بْنُ عَمْرِو بْنِ عَبَّادِ بْنِ جَبَلَةَ بْنِ أَبِي رَوَّادٍ، حَدَّثَنَا حَرَمِيُّ بْنُ عُمَارَةَ، حَدَّثَنَا شَدَّادٌ أَبُو طَلْحَةَ الرَّاسِبِيُّ، عَنْ غَيْلاَنَ بْنِ جَرِيرٍ، عَنْ أَبِي بُرْدَةَ، عَنْ أَبِيهِ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ ‏ "‏ يَجِيءُ يَوْمَ الْقِيَامَةِ نَاسٌ مِنَ الْمُسْلِمِينَ بِذُنُوبٍ أَمْثَالِ الْجِبَالِ فَيَغْفِرُهَا اللَّهُ لَهُمْ وَيَضَعُهَا عَلَى الْيَهُودِ وَالنَّصَارَى ‏"‏ ‏.‏ فِيمَا أَحْسِبُ أَنَا ‏.‏ قَالَ أَبُو رَوْحٍ لاَ أَدْرِي مِمَّنِ الشَّكُّ ‏.‏ قَالَ أَبُو بُرْدَةَ فَحَدَّثْتُ بِهِ عُمَرَ بْنَ عَبْدِ الْعَزِيزِ فَقَالَ أَبُوكَ حَدَّثَكَ هَذَا عَنِ النَّبِيِّ صلى الله عليه وسلم قُلْتُ نَعَمْ ‏.‏
Reference : Sahih Muslim 2767 d
In-book reference : Book 50, Hadith 60
USC-MSA web (English) reference : Book 37, Hadith 6668
  (deprecated numbering scheme)