Is it permissible for a Muslim to pray the 'Isha (night) prayer early based on the timing of another mosque, given the difference in prayer times between mosques in the German city of Essen, and his desire to pray before going to work?

The fundamental principle for determining prayer times is the Sharia (definition)-compliant signs. Jurists may differ in interpreting some of these signs. For instance, the majority view is that the time for the Isha prayer begins with the disappearance of the red twilight (shafaq al-ahmar), whereas Abu Hanifa holds that it begins with the disappearance of the whiteness that follows the red twilight.

Today, people rely on written calendars to determine prayer times due to the difficulty of verifying the Sharia-compliant signs in cities. Correct calendars are those that correspond to the Sharia-compliant signs or were prepared based on observation and under the supervision of scholars.

When calendars differ and the most accurate one is unknown, the later time should be followed, as prayer is not to be performed until the entry of its time is verified or highly presumed.