Fasting: A Prisoner Who Cannot Be Certain About the Month of Ramadan
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 1706
If a prisoner cannot be certain about whether or not it is the month of Ramadan, he must act according to his supposition; and if he can find a stronger supposition, he cannot act on the weaker supposition. Furthermore, he must endeavour to attain the strongest probability; if there is no other way, he must as a final resort draw lots (qurʿah) if this results in strengthening his inclination. If acting according to supposition is not possible, he must fast a month that he deems is probably the month of Ramadan. Moreover, he must bear that month in mind and if he finds out afterwards that the month he fasted was after the month of Ramadan, there is no obligation for him; however, if it becomes known that it was before the month of Ramadan, he must make up the fasts of the month of Ramadan.