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

And what was narrated by Ahmad bin Muhammad bin ‘Isa, from Mu‘awiyah bin Hakim, from Muhammad bin Abi Umayr, from Hammad al-Nabb, from ‘Ammar al-Sabati, who said: I asked Abu Abdillah عليه السلام, peace be upon him, about a man who does not know whether he prayed two rak‘ahs or one in the Fajr prayer. Imam عليه السلام said: "He should recite the tashahhud and conclude (the prayer), then stand and pray one rak‘ah. If he had prayed two rak‘ahs, then this (extra) rak‘ah is a recommended prayer (nafilah), and if he had prayed only one rak‘ah, then this is the completion of the prayer." I asked: "And what if he prayed Maghrib and does not know whether he prayed two rak‘ahs or three?" Imam عليه السلام said: "He should recite the tashahhud and conclude (the prayer), then stand and pray one rak‘ah. If he had prayed three, then this (extra) rak‘ah is a recommended prayer (nafilah), and if he had prayed two, then this is the completion of the prayer. And by Allah سبحانه وتعالى, this is something that is never made up (qadah’)."