Congregational Prayer and Its Virtue
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 57
وَ رَوَى عَبْدُ اَللَّهِ بْنُ سِنَانٍ عَنْهُ عَلَيْهِ اَلسَّلاَمُ أَنَّهُ قَالَ: «مَا مِنْ عَبْدٍ يُصَلِّي فِي اَلْوَقْتِ وَ يَفْرُغُ ثُمَّ يَأْتِيهِمْ وَ يُصَلِّي مَعَهُمْ وَ هُوَ عَلَى وُضُوءٍ إِلاَّ كَتَبَ اَللَّهُ لَهُ خَمْساً وَ عِشْرِينَ دَرَجَةً.
Abdullah ibn Sinan narrated from Imam عليه السلام who said: "There is no servant who prays at the prescribed time, completes it, then joins another group and prays with them while still in a state of wudu' except that Allah سبحانه وتعالى writes for him twenty-five degrees (levels of reward)."
- Ṣaḥīḥ al-Faqīh