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

Al-Husayn bin Sa‘id, from Ibn Abi Umayr, from Hammad and al-Hakam bin Miskin, from ‘Ammar al-Sabati, who said: I said to Abu Abdillah عليه السلام, peace be upon him: “A man doubts in the Maghrib prayer and does not know whether he has prayed two rak‘ahs or three.” Imam عليه السلام said: "He performs the taslim, then stands and adds to it one rak‘ah." Then Imam عليه السلام said: "By Allah سبحانه وتعالى, this is something that is never made up (qadha)."