The World Federation One Stop Fiqh

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. And 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 it was indeed the month of Ramadan, or it was after it, there is no obligation on 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.