Congregational Prayer and Its Virtue
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 57
وَ رَوَى اَلْحُسَيْنُ بْنُ يَسَارٍ أَنَّهُ سَمِعَ مَنْ يَسْأَلُ اَلرِّضَا عَلَيْهِ اَلسَّلاَمُ: عَنْ رَجُلٍ صَلَّى إِلَى جَانِبِ رَجُلٍ فَقَامَ عَنْ يَسَارِهِ وَ هُوَ لاَ يَعْلَمُ كَيْفَ يَصْنَعُ إِذَا عَلِمَ وَ هُوَ فِي اَلصَّلاَةِ قَالَ «يُحَوِّلُهُ إِلَى يَمِينِهِ.
Al-Hussain ibn Yasar narrated that he heard someone asking Imam Al-Ridha عليه السلام about a man who was praying next to another man and stood on his left side without knowing what to do upon realizing this during the prayer. Imam عليه السلام said: "He should move him to his right side."
- Ṣaḥīḥ al-Faqīh