Congregational Prayer and Its Virtue
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 57
وَ سَأَلَ عَمَّارٌ اَلسَّابَاطِيُّ أَبَا عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ: عَنْ رَجُلٍ أَدْرَكَ اَلْإِمَامَ حِينَ يُسَلِّمُ قَالَ «عَلَيْهِ أَنْ يُؤَذِّنَ وَ يُقِيمَ وَ يَفْتَتِحَ اَلصَّلاَةَ.
Ammar al-Sabati asked Imam Jafar ibn Muhammad Al-Sadiq عليه السلام about a man who arrives at the mosque just as the Imam is concluding the prayer with the taslim (final salutation). Imam عليه السلام replied: "He should give the adhan (call to prayer), make the iqamah (call to commence the prayer), and then begin his prayer."
- Ṣaḥīḥ al-Faqīh