Congregational Prayer and Its Virtue
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 57
وَ سَأَلَ عُمَرُ بْنُ يَزِيدَ، أَبَا عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ: عَنِ اَلرِّوَايَةِ اَلَّتِي يَرْوُونَ أَنَّهُ لاَ يَنْبَغِي أَنْ يُتَطَوَّعَ فِي وَقْتِ كُلِّ فَرِيضَةٍ مَا حَدُّ هَذَا اَلْوَقْتِ فَقَالَ «إِذَا أَخَذَ اَلْمُقِيمُ فِي اَلْإِقَامَةِ» فَقَالَ لَهُ إِنَّ اَلنَّاسَ يَخْتَلِفُونَ فِي اَلْإِقَامَةِ قَالَ «اَلْمُقِيمُ اَلَّذِي يُصَلَّى مَعَهُ.
Umar ibn Yazid asked Imam Jafar ibn Muhammad Al-Sadiq عليه السلام about the narration that states it is not appropriate to perform supererogatory (nafl) prayers at the time of every obligatory (fardh) prayer. He asked: "What is the limit for this time?" He عليه السلام replied: "When the person giving the iqamah (call immediately preceding the prayer) begins the iqamah." Umar said: "People differ in the timing of the iqamah." He عليه السلام responded: "The one giving the iqamah is the one with whom the prayer is being established”.
- Ṣaḥīḥ al-Faqīh, p. 54