كتاب الْمَسَاجِدِ وَمَوَاضِعِ الصَّلاَةِ
5  
The Book of Mosques and Places of Prayer
(42)
Chapter: The virtue of prayer in congregation, and clarifying the stern warning against staying away from it, and that it is fard kifayah
(42)
باب فَضْلِ صَلاَةِ الجَمَاعَةِ وَبَيَانِ التَّشْدِيدِ فِي التَّخَلُّفِ عَنْهَا ‏
Sahih Muslim 649 d

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

Prayer said in a congregation is equivalent to twenty-five (prayers) as compared with the prayer said by a single person.
وَحَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ بْنِ قَعْنَبٍ، حَدَّثَنَا أَفْلَحُ، عَنْ أَبِي بَكْرِ بْنِ مُحَمَّدِ بْنِ عَمْرِو بْنِ حَزْمٍ، عَنْ سَلْمَانَ الأَغَرِّ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ صَلاَةُ الْجَمَاعَةِ تَعْدِلُ خَمْسًا وَعِشْرِينَ مِنْ صَلاَةِ الْفَذِّ ‏"‏ ‏.‏
Reference : Sahih Muslim 649d
In-book reference : Book 5, Hadith 308
USC-MSA web (English) reference : Book 4, Hadith 1363
  (deprecated numbering scheme)