Is it permissible to pray according to the calendar of the Union of Islamic Organizations of France, or the Umm Al-Qura calendar, instead of the calendar of the Muslim Scholars Association, knowing that the timing differs by more than an hour?

The time for 'Isha prayer begins when the red twilight disappears. If it is possible to ascertain the time by this sign, then it should be acted upon. If that is not possible, then if the calendar of the Union of Islamic Organizations in France or the Umm al-Qura calendar provides certainty or a strong presumption that the time has begun, prayer is permissible based on it. However, if that is not achieved, then prayer is not permissible based on it, because the validity of the prayer depends on certainty or a strong presumption that its time has begun. Therefore, whoever doubts the beginning of the time should not pray until they are certain or have a strong presumption of it.