Congregational Prayer and Its Virtue
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 57
وَقَالَ عَلَيْهِ اَلسَّلاَمُ: «أَتِمُّوا صُفُوفَكُمْ إِذَا رَأَيْتُمْ خَلَلاً وَ لاَ يَضُرُّكَ أَنْ تَتَأَخَّرَ وَرَاءَكَ إِذَا وَجَدْتَ ضِيقاً فِي اَلصَّفِّ اَلْأَوَّلِ إِلَى اَلصَّفِّ اَلَّذِي خَلْفَكَ وَ تَمْشِيَ مُنْحَرِفاً.
Imam عليه السلام said: "Complete your rows when you see a gap, and it does not harm you to move back if you find tightness in the first row to the row behind you, walking at an angle."
- Ṣaḥīḥ al-Faqīh