Is it permissible to pray Fajr before the Adhan when traveling?

The time for Fajr prayer begins with the appearance of true dawn. Prayer is not valid before its prescribed time, as Allah Almighty says: "Indeed, prayer has been decreed upon the believers a time-bound ordinance." It is permissible for someone who does not know the prayer time to follow a trustworthy muezzin who is knowledgeable of the time.