What is the ruling on someone who is overcome by sleep after hearing the alarm for Fajr prayer, and will they be rewarded for the prayer with the intention of waking up for it if they did not hear the alarm?

There is no sin upon one who does not wake up for prayer, even if they heard the alarm, because they are in the state of a sleeper, and the pen has been lifted from them. However, if they wake up and are lazy about praying, they must seek forgiveness. As for one who did not hear the alarm at all, there is no sin upon them after having taken the necessary precautions. The attainment of reward is possible if a Muslim intends good but misses it without fault. So, whoever's habit was to perform acts of obedience but was prevented from doing so by an irresistible cause, the reward for it will be written for them.