Congregational Prayer and Its Virtue
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 57
وَ رَوَى مُحَمَّدُ بْنُ سَهْلٍ عَنْ أَبِيهِ قَالَ: سَأَلْتُ اَلرِّضَا عَلَيْهِ اَلسَّلاَمُ عَمَّنْ رَكَعَ مَعَ إِمَامِ قَوْمٍ يُقْتَدَى بِهِ ثُمَّ رَفَعَ رَأْسَهُ قَبْلَ اَلْإِمَامِ قَالَ «يُعِيدُ رُكُوعَهُ مَعَهُ.
Muhammad ibn Sahl narrated from his father who said: “I asked Imam Al-Ridha عليه السلام about a person who bows (in ruku') with an Imam of a congregation who is followed, and then raises his head before the Imam.” Imam عليه السلام replied: "He should repeat his bowing (ruku') with him."
- Ṣaḥīḥ al-Faqīh, p. 56