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)

Muhammad ibn Yaqub narrated from Ali ibn Ibrahim from his father from Muhammad ibn Isa from Yunus from a man from Abu Abdillah عليه السلام, peace be upon him, who said: I asked Imam al-Sadiq عليه السلام about an imam (of prayer) who is leading four or five people in prayer. Then two of them do tasbih (declare the imam of prayer has prayed three rak’ahs), and three of them do tasbih that they have prayed four rak’ahs. The two say: “Stand up,” and the three say: “Sit down,” while the imam (of prayer) inclines toward one of the groups or is uncertain and neutral in his doubt what is obligatory upon him? Imam عليه السلام said: “There is no sahw (prostration of forgetfulness) upon the imam (of prayer) if those behind him have preserved his error with certainty. And there is no sahw upon those behind the imam (of prayer), if the imam (of prayer) did not err. And there is no sahw in sahw (no prostration for doubting whether one made a mistake). And there is no sahw in the Maghrib and Fajr prayers, nor in the first two rak’ahs of any prayer, and there is no sahw in supererogatory (nafilah) prayers. But if those behind the imam (of prayer) differ among themselves, then it is obligatory upon him and upon them, by way of precaution, to repeat the prayer and to act upon certainty.”