Chapter on the Virtue of Mosques and Prayer Within Them, and the Virtue of Congregational Prayer and Its Rulings

Sa’ad from Abu Ja’far from al-Hasan ibn Ali ibn Faddal, who said: I wrote to Imam al-Ridha عليه السلام, peace be upon him, regarding a man who was behind the imam (of prayer), following him, and he bowed before the imam (of prayer), thinking that the imam (of prayer) had bowed. Then, when he saw that the imam (of prayer) had not bowed, he raised his head and then repeated the bowing with the imam (of prayer). Does this invalidate his prayer, or is the rak’ah valid for him? Imam عليه السلام wrote: “He completes his prayer, and what he did does not invalidate his prayer.”