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

Muhammad bin Ya‘qub, from Muhammad bin Isma‘il, from al-Fadl bin Shadhan, and Ali bin Ibrahim, from his father, all from Hammad bin ‘Isa, from Hariz, from Zurarah, from one of them (Imams عليه السلام), peace be upon them both, who said: I said to Him عليه السلام: “A man does not know whether he prayed one rak‘ah or two.” Imam عليه السلام said: "He should repeat (the prayer)."