Prayer Times for a Prisoner Who Cannot Distinguish Day from Night - Jurisprudential Answers - Book of Prayer

Ahmed al-Hasan Response:

If he can form a belief or even a probability that the prayer time has begun, he acts and performs his obligations according to that belief or probability. If he cannot form even a probability, he distributes the five obligatory prayers over the period in which he is awake as follows: when he wakes from sleep, he performs Fajr; before he sleeps, he performs Maghrib and Isha; and between them-that is, between Fajr and Maghrib-he performs Dhuhr and Asr.