Sunan Ibn Majah, Volume 1, Book 4, Hadith 788 (DarusSalam) ⓘ
It was narrated that Abu Sa'eed Al-Khudri said: "The Messenger of Allah said: 'the prayer of a man in congregation is twenty-five levels higher than his prayer in his home.'"
حَدَّثَنَا أَبُو كُرَيْبٍ، حَدَّثَنَا أَبُو مُعَاوِيَةَ، عَنْ هِلاَلِ بْنِ مَيْمُونٍ، عَنْ عَطَاءِ بْنِ يَزِيدَ، عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " صَلاَةُ الرَّجُلِ فِي جَمَاعَةٍ تَزِيدُ عَلَى صَلاَتِهِ فِي بَيْتِهِ خَمْسًا وَعِشْرِينَ دَرَجَةً " .
also referenced under: Hadith 788 (Reference) & Book 4, Hadith 54 (In-Book)