Chapter on Rulings on Forgetfulness (Sahw) in Prayer and What Requires Repeating of Prayer

Fadalah, from Rifa‘ah, who said: I asked Abu Abdillah عليه السلام, peace be upon him, about a man who does not know whether he prayed one rak‘ah or two. Imam عليه السلام said: "He should repeat (the prayer)."