Sa’ad ibn Abdullah, from al-Hasan ibn Ali, from Abdullah ibn al-Mughirah, from Ubays ibn Hisham, from Aban ibn Uthman, from Abd al-Rahman ibn Abi Abdullah, from Abu Abdillah عليه السلام, peace be upon him, who said: I (narrator) said to Imam عليه السلام: “A man was taken captive by the Romans, and he did not fast the month of Ramadan, and he did not know which month it was.” Imam عليه السلام said: “He should fast a month, seeking to determine it, and count it thereby. If the month which he fasted was before (month of) Ramadan, it will not suffice him, and if it was after the month of Ramadan, it will suffice him.”