Is expiation (kaffarah) obligatory for one who swore to wake up for Fajr prayer but was overcome by sleep and did not hear the alarm?

If someone takes an oath to do something but does not do it due to forgetfulness, ignorance, sleep, or an unconscious state, then he does not break his oath. This is because he is excused due to his mind being overwhelmed, and no expiation is required of him.