What is the ruling on missing Fajr prayer if one did not hear the Adhan?

A Muslim must know that intentionally delaying the prayer beyond its prescribed time is a grave sin and a serious transgression. As for sleeping, provided one takes measures to wake up, it is a valid excuse that removes accountability. The sleeping person should take measures that help them wake up for prayer, such as setting an alarm or appointing someone to wake them. Scholars have differed regarding the obligation of taking these measures. Many of them held that it is not obligatory, while others, including the eminent scholar Al-Uthaymeen, maintained that it is obligatory, and that whoever neglects it incurs sin and is exposed to the warning. The proof for the obligation of taking measures is the Prophet's (peace be upon him) saying: "If you can manage not to be overcome in prayer before the rising of the sun and before its setting, then do so." As for missing congregational prayer due to not hearing the call to prayer, there is no accountability for that, because congregational prayer is obligatory only for those who hear the call.