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

Ahmad ibn Muhammad from Ibn Abi Umayr from Hammad ibn Uthman from Ubaydullah al-Halabi: Abu Abdillah عليه السلام, peace be upon him, (was asked) regarding a man who is standing behind the Imam (of prayer) and the Imam (of prayer) prolongs the tashahhud. Imam عليه السلام said: “He may give salam behind him and go about his need if he wishes.”