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)

Sa’ad ibn Abdillah from Ahmad ibn al-Hasan ibn Ali ibn Faddal from Amr ibn Said from Musaddiq ibn Sadaqah from Ammar al-Sabati, who said: I asked Aba Abdillah عليه السلام, peace be upon him, about a man who performs the obligatory prayer, then finds a group of people praying in congregation is it permissible for him to repeat the prayer with them? Imam عليه السلام said: “Yes, and it is better.” I said: “And if he does not do it?” Imam عليه السلام said: “There is no harm.”