Congregational Prayer and Its Virtue
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 57
وَ رَوَى اَلْحَلَبِيُّ عَنْ أَبِي عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ أَنَّهُ قَالَ: «إِذَا صَلَّيْتَ خَلْفَ إِمَامٍ تَأْتَمُّ بِهِ فَلاَ تَقْرَأْ خَلْفَهُ سَمِعْتَ قِرَاءَتَهُ أَوْ لَمْ تَسْمَعْ إِلاَّ أَنْ تَكُونَ صَلاَةً يُجْهَرُ فِيهَا بِالْقِرَاءَةِ فَلَمْ تَسْمَعْ فَاقْرَأْ.
Al-Halabi narrated from Imam Jafar ibn Muhammad Al-Sadiq عليه السلام that He said: "If you are praying behind an Imam whom you are following, do not recite (the Qur'an) behind him, whether you hear his recitation or not, except in a prayer where the recitation is done aloud and you do not hear it—then you may recite."
- Ṣaḥīḥ al-Faqīh