Chapter on the Rulings of Congregational Prayer (the Minimum Number for Congregational Prayer, the Description of the Imam, Who Is to Be Followed and Who Is Not to Be Followed, Recitation Behind Both of Them, the Rulings of Those Led in Prayer, and Other Such Rulings Related to It)

Al-Husayn ibn Said narrated from Safwan ibn Yahya and Fadalah ibn Ayyub, from al-Ala’ ibn Razin, from Muhammad ibn Muslim, from Abu Ja’far عليه السلام, peace be upon him, who said: I asked Imam al-Baqir عليه السلام about a man who leads a group in prayer while he is without ritual purity, and he does not realize it until after his prayer is finished. Imam عليه السلام said: “He must repeat (his prayer), but those behind him do not need to repeat theirs, even if he informs them that he was without ritual purity.”