Congregational Prayer and Its Virtue
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 57
وَ قَدْ قَالَ اَلنَّبِيُّ صَلَّى اَللَّهُ عَلَيْهِ وَ آلِهِ: «اَلْمُؤْمِنُ وَحْدَهُ حُجَّةٌ وَ اَلْمُؤْمِنُ وَحْدَهُ جَمَاعَةٌ.
The Prophet said: "A believer alone is a proof (Hujjah), and a believer alone is a congregation."
- Ṣaḥīḥ al-Faqīh