Is it permissible to pray Isha in congregation at home an hour and a half after sunset to ensure its time has begun, due to the inaccuracy of available calendars?

The fundamental principle for determining the start of prayer times is the appearance of physical, শরিয়াহ-prescribed signs. Scholars have relied on these signs to establish prayer times and have not depended on astronomical calculations for this purpose, although calculations are used for other matters such as determining the number of years and the lunar months. Some contemporary scholars permit reliance on calendars in large cities where it is difficult to discern the Shar'i signs due to artificial lights, while emphasizing the importance of careful verification and taking precautions. One should not miss congregational prayer in the mosque based solely on the mere possibility that the time has begun according to calculations.