Congregational Prayer and Its Virtue
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 57
وروى زرارة عن أبي جعفر عليه السلام أنه قال: " إذا أقيمت الصلاة حرم الكلام على الامام وأهل المسجد إلا في تقديم إمام.
Zurarah narrated from Imam Muhammad ibn Ali Al-Baqir عليه السلام that He said: "When the prayer has been established (by the iqamah), speaking becomes forbidden for the Imam and the people of the mosque, except in the matter of appointing an Imam”.
- Ṣaḥīḥ al-Faqīh, p. 54