If a captive fasts without a strong presumption of Ramadan commencing, is the fast valid if it happens to coincide?
General Chapter
Al-Mughni
Book of Fasting
Primary text
If a captive fasts without a strong presumption that Ramadan has begun, his fast is invalid, even if it coincides with Ramadan, because he fasted based on doubt, analogous to intending on the Day of Doubt that tomorrow is Ramadan and obligatory. However, if the presumption is strong without a clear sign, some scholars hold that fasting is required, and make-up is due once the month is known, similar to being uncertain of the Qibla direction.
Supporting text
The apparent view of Al-Kharqi is that one should strive (taharrā), and if the entry of the month is strongly presumed, the fast is valid, even without explicit proof, as one is not burdened beyond capacity. This is similar to the ruling on the Qibla.