Congregational Prayer and Its Virtue
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 57
وَ فِي رِوَايَةِ عُبَيْدِ بْنِ زُرَارَةَ عَنْهُ عَلَيْهِ اَلسَّلاَمُ: «أَنَّهُ إِنْ سَمِعَ اَلْهَمْهَمَةَ فَلاَ يَقْرَأْ.
In a narration from Ubayd ibn Zurarah from Imam عليه السلام: "If he (the follower) hears a murmur (of the Imam's recitation), he should not recite."
- Ṣaḥīḥ al-Faqīh