Congregational Prayer and Its Virtue
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 57
وَ رَوَى إِسْحَاقُ بْنُ عَمَّارٍ عَنْ أَبِي عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ أَنَّهُ قَالَ: «يَنْبَغِي لِلْإِمَامِ أَنْ يَكُونَ صَلاَتُهُ عَلَى صَلاَةِ أَضْعَفِ مَنْ خَلْفَهُ.
Ishaq ibn Ammar narrated from Imam Jafar ibn Muhammad Al-Sadiq عليه السلام that He said: "It is appropriate for the Imam's prayer to be suited to the ability of the weakest among those behind him."
- Ṣaḥīḥ al-Faqīh