Is it permissible for the first call to Fajr prayer to be made an hour before the actual second call, considering the harm this entails for those who work morning shifts?

The first Adhan for Fajr is a Sunnah, and its time is a matter of scholarly disagreement. Some scholars believe it occurs during the time of sahar (pre-dawn meal), between the false dawn and the true dawn. Others believe it begins from the second half of the night. Therefore, the Adhan one hour before Fajr is permissible. A Muslim should benefit from it by rising for ablution, performing the Witr prayer, and making du'a (supplication), then returning to sleep until the Fajr Adhan. This brings him the reward of the hereafter and strength in this world. It has been reported that dhikr (remembrance of Allah) gives strength to the one who performs it, such as tasbih (subhanallah), tahmid (alhamdulillah), and takbir (Allahu Akbar) before sleep, due to its effect on strengthening the body and soul.