كتاب الإيمان
1
The Book of Faith
(94)
Chapter: The Evidence that groups of Muslims will enter Paradise without being called to account, and without being punished
(94)
باب الدَّلِيلِ عَلَى دُخُولِ طَوَائِفَ مِنَ الْمُسْلِمِينَ الْجَنَّةَ بِغَيْرِ حِسَابٍ وَلاَ عَذَابٍ ‏‏

Abu Hazim narrated it on the authority of Ibn Sa'd that the Messenger of Allah (ﷺ) said:

Seventy thousand persons or seven hundred thousand persons (Abu Hazim does not remember the exact number) would enter Paradise holding and supporting one another, and the first among them would not enter till the last among them would enter (therein) ; (they would enter simultaneously) and their faces would be bright like the full moon.
حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا عَبْدُ الْعَزِيزِ، - يَعْنِي ابْنَ أَبِي حَازِمٍ - عَنْ أَبِي حَازِمٍ، عَنْ سَهْلِ بْنِ سَعْدٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏ "‏ لَيَدْخُلَنَّ الْجَنَّةَ مِنْ أُمَّتِي سَبْعُونَ أَلْفًا أَوْ سَبْعُمِائَةِ أَلْفٍ - لاَ يَدْرِي أَبُو حَازِمٍ أَيَّهُمَا قَالَ - مُتَمَاسِكُونَ آخِذٌ بَعْضُهُمْ بَعْضًا لاَ يَدْخُلُ أَوَّلُهُمْ حَتَّى يَدْخُلَ آخِرُهُمْ وُجُوهُهُمْ عَلَى صُورَةِ الْقَمَرِ لَيْلَةَ الْبَدْرِ ‏"‏ ‏.‏
Reference : Sahih Muslim 219
In-book reference : Book 1, Hadith 434
USC-MSA web (English) reference : Book 1, Hadith 424
  (deprecated numbering scheme)