Congregational Prayer and Its Virtue
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 57
وَ رَوَى عُبَيْدُ اَللَّهِ بْنُ عَلِيٍّ اَلْحَلَبِيُّ عَنْ زُرَارَةَ عَنْ أَبِي عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ قَالَ: سَأَلْتُهُ عَنِ اَلرَّجُلِ يَكُونُ خَلْفَ اَلْإِمَامِ فَيُطِيلُ اَلْإِمَامُ اَلتَّشَهُّدَ قَالَ «يُسَلِّمُ وَ يَمْضِي لِحَاجَتِهِ إِنْ أَحَبَّ.
Ubaydullah ibn Ali Al-Halabi narrated from Zurarah from Imam Jafar ibn Muhammad Al-Sadiq عليه السلام who said: I asked him about a person who is behind the Imam, and the Imam prolongs the tashahhud (sitting for testimony). Imam عليه السلام said: "He may perform the taslim (salutation of peace) and leave if he wishes."
- Ṣaḥīḥ al-Faqīh, p. 56