Chapter on the Rulings on Forgetfulness (Ahkam al-Sahw)

As for what was narrated by Sa‘d ibn Abdullah from Ibn Abi Najran from al-Husayn ibn Sa‘id from Hammad from Hariz from Abu Ja‘far عليه السلام, peace be upon him, who said: I asked Imam عليه السلام about a man who prayed two rak‘ahs in Kufa, then remembered, while he was in Mecca, or in Medina, or in Basra, or in another town among the towns, that he had only prayed two rak‘ahs. Imam عليه السلام said: "He should pray two rak‘ahs."