Sheikh Ibn Uthaimin (may Allah have mercy on him) was asked the following question: "May Allah reward you with the best for your advice. The questioner says: "In the month of Ramadan, there are differences between the imams of different mosques regarding the determination of the dawn of Fajr. It should be added that there is a prayer time calendar in these mosques, which was created by astronomers commissioned by the Ministry of Religion. However, there are some imams who do not follow this calendar. Especially at the Fajr prayer, they delay the call to prayer by an average of more than fifteen minutes compared to the calendar, considering that the dawn of Fajr cannot be observed due to electric lamps. What is your advice regarding these imams and what is your view on astronomers? May Allah reward you."
The honorable Sheikh Ibn Uthaimin (may Allah have mercy on him) said: "There is no doubt that astronomers are knowledgeable in their field, but Allah (the Exalted) says: 'And eat and drink until the white thread of dawn becomes distinct to you from the black thread [of night].' (Quran 2:187). That is, as long as the dawn (Fajr) is not visible, one can eat and drink. The problem nowadays is that the residents of cities and villages where electric lights are available are not able to observe the dawn of Fajr from the beginning, which is due to the presence of lights. As a precaution, one should stop eating and drinking at the time of Fajr according to the prayer time calendar. Regarding prayer, it should be performed in such a way that it is not done too early. Waiting for prayer, praised be to Allah, to confirm the time, is not counted as delaying the prayer beyond the prescribed time. The caution in this case refers to fasting, so we say: caution (in fasting) means following the prayer time calendar. Regarding prayer, one should delay it until the dawn of Fajr is observed."حكم تأخير أذان الفجر ربع ساعة عن التقويم..