Congregational Prayer and Its Virtue
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 57
وَقَالَ اَلصَّادِقُ عَلَيْهِ اَلسَّلاَمُ: «ثَلاَثَةٌ لاَ يُصَلَّى خَلْفَهُمُ اَلْمَجْهُولُ وَ اَلْغَالِي وَ إِنْ كَانَ يَقُولُ بِقَوْلِكَ وَ اَلْمُجَاهِرُ بِالْفِسْقِ وَ إِنْ كَانَ مُقْتَصِداً.
Imam Jafar ibn Muhammad Al-Sadiq عليه السلام said: "Three people should not be prayed behind: the one who is unknown (al-majhūl), the extremist (al-ghālī) even if he claims to hold your beliefs, and the one who openly commits sinful acts (al-mujāhir bil-fisq) even if he appears moderate."
- Ṣaḥīḥ al-Faqīh