Congregational Prayer and Its Virtue
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 57
وَقَالَ أَبُو اَلْمَغْرَاءِ حُمَيْدُ بْنُ اَلْمُثَنَّى: كُنْتُ عِنْدَ أَبِي عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ فَسَأَلَهُ حَفْصٌ اَلْكَلْبِيُّ فَقَالَ أَكُونُ خَلْفَ اَلْإِمَامِ وَ هُوَ يَجْهَرُ بِالْقِرَاءَةِ فَأَدْعُو وَ أَتَعَوَّذُ قَالَ «نَعَمْ فَادْعُ.
Abu al-Maghra' Humayd ibn al-Muthanna said: "I was with Imam Jafar ibn Muhammad Al-Sadiq عليه السلام when Hafs al-Kalbi asked him: "When I am behind the Imam and he is reciting aloud, may I make supplications and seek refuge (in Allah سبحانه وتعالى)?" Imam عليه السلام said: "Yes, you may supplicate."
- Ṣaḥīḥ al-Faqīh, p. 58