Is it permissible to perform Fajr prayer in congregation at the mosque if the time for its establishment is very early, before the true time of Fajr Sadiq (true dawn) enters, especially in Ramadan, knowing that Fajr Sadiq is delayed by about 35 minutes after the Adhan?

It is advisable to discuss with the mosque community the possibility of delaying the prayer until any doubt about the entry of its time is removed. If they insist on the current time, and the doubt is based on clear indicators, the prayer can be delayed without causing disruption to the people, and official bodies should be contacted to verify the matter. It is known that the determination of prayer times in calendars is based on precise astronomical calculations, and it is originally a joint effort between astronomers and jurists. It should be noted that people differ in observing the appearance of dawn (Fajr); some do not discern it until it becomes clear, while others discern it as soon as it appears. It is legislated to perform the Fajr prayer at the beginning of its time (at taghlees - before full daylight), and this is what the Prophet, peace and blessings be upon him, and the Companions used to do, and it is the view of Malik and Shafi'i. The determining factor is the actual appearance of dawn, not the calendar or astronomical calculations.