Narrated by:`Abdullah bin `Umar
Narrated `Abdullah bin `Umar:The reward of the congregational prayer is twenty seven times greater (than that of the prayer offered by a person alone).
قَالَ شُعَيْبٌ وَحَدَّثَنِي نَافِعٌ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، قَالَ تَفْضُلُهَا بِسَبْعٍ وَعِشْرِينَ دَرَجَةً.
Bukhari
Call to Prayers (Adhaan) • Hadith 46