Congregational Prayer and Its Virtue
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 57
1147 - وَ سَأَلَ مُوسَى بْنُ بَكْرٍ أَبَا اَلْحَسَنِ مُوسَى بْنَ جَعْفَرٍ عَلَيْهِمَا اَلسَّلاَمُ: عَنِ اَلرَّجُلِ يَقُومُ فِي اَلصَّفِّ وَحْدَهُ قَالَ «لاَ بَأْسَ إِنَّمَا يَبْدُو اَلصَّفُّ وَاحِداً بَعْدَ وَاحِدٍ.
Hadith.1147 - Musa ibn Bakr asked Abu Al-Hasan Imam Musa ibn Jafar Al-Kadhim عليه السلام about a man who stands alone in a row during prayer.
Imam عليه السلام said: "There is no problem ; indeed, the row is formed one person at a time."