Does expiation become obligatory for someone who swore to pray Fajr on time, then prayed it after sunrise on two days of the week?

Performing the prayer on time is obligatory. If someone swears to do so and then breaks their oath, expiation becomes due. Jurists have stipulated that whoever swears to perform an obligatory act and then breaks their oath must offer expiation. However, if the delay is due to sleep, jurists have differed on this matter. The soundest opinion is that one does not break their oath if they sleep before the time of the prayer begins and wake up after it has ended. But if they sleep after the time of the prayer has begun, then they do break their oath. Offering expiation is more cautious and absolves one of responsibility.