صَحِيحُ مُسْلِمٍ
Sahih Muslim 650 a
The Book of Mosques and Places of Prayer
The virtue of prayer in congregation, and clarifying the stern warning against staying away from it, and that it is fard kifayah
حَدَّثَنَا يَحْيَى بْنُ يَحْيَى، قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ صَلاَةُ الْجَمَاعَةِ أَفْضَلُ مِنْ صَلاَةِ الْفَذِّ بِسَبْعٍ وَعِشْرِينَ دَرَجَةً .
Ibn Umar reported Allah's Messenger (ﷺ) assaying: Prayer said in a congregation is twenty-seven degrees more excellent than prayer said by a single person.
Sahih Muslim, 650 aSahihصحيح