How can a prisoner pray while in a dark underground room, restrained, and unaware of prayer times or when the month of Ramadan begins?

If a person does not know the signs for prayer and fasting times, they should exert effort and investigate to perform the five prayers in order, estimating the time between them, and pray according to their condition, even if by gesturing. Similarly for fasting, they should fast with effort and investigation until they are reasonably sure they have completed a day, and then complete a month according to their estimation, based on the Almighty's saying: "And We do not burden a soul beyond its capacity." If the months become unclear to a prisoner, it is obligatory for them to investigate and fast. If their fasting coincides with the month [of Ramadan] or a later month, it suffices. If their fasting coincides with an incomplete month, and people fasted a full month, there are two opinions: it suffices for them, or they must fast another day. If their fasting coincides with a month before Ramadan, the majority of jurists hold that it is not sufficient, because they performed the act of worship before its cause of obligation came into existence.