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)

So this is a solitary (shadh) report that contradicts all the other reports, and its ruling is such that it is not permissible to act upon it. Moreover, it contains within it what invalidates it that the Commander of the Faithful عليه السلام, peace be upon him, performed an obligatory prayer without purity, being unaware of that, and we hold certainty that such a thing is impossible due to the indication of his infallibility, peace be upon him. Muhammad ibn Ali ibn al-Husayn also mentioned: “I heard a group of our elders say that the people are not required to repeat anything from the prayers in which the recitation is done aloud, but they are required to repeat the prayers that he led in which the recitation was not done aloud. And likewise, if someone led them in prayer and it later became clear that he was not of their religion, then they are not required to repeat any of the prayers they performed behind him.”