What is the ruling on praying in a mosque where the 'Isha prayer is offered forty-five minutes before the legal time for the athan, on the pretext that the twilight has disappeared, while the sky is still blue and the twilight has not yet disappeared?

The time for 'Isha prayer begins at the disappearance of the red twilight (shafaq), which is a cosmic sign indicating the entry of 'Isha time. Al-Nawawi narrated from Imam Al-Shafi'i that the time for 'Isha enters when the redness vanishes, and whoever prays while the redness remains must repeat the prayer. Sheikh Al-Islam Ibn Taymiyyah holds that the time for 'Isha is the disappearance of the red twilight, and it is cautious to wait for the disappearance of the whiteness to ensure the redness has vanished. This is the madhhab of the majority, such as Malik, Al-Shafi'i, and Ahmad, while Abu Hanifa holds that the shafaq is the whiteness. Based on this, if the congregants of the mosque pray after the disappearance of the twilight, their prayer is valid, and the sky being blue is an indication of the red twilight's disappearance.