Sheikh Ḥusain Ibn ‘Awdah Al ‘Awāyshah said that whoever lets a prayer go until the next one begins while he is awake without an excuse mentioned in the Sharī’ah (Islamic Law) is neglectful. So, anybody who sleeps through a prayer or forgets it is not neglectful. Such a person prays what he has missed when he remembers the prayer. This is the only expiation, i.e. that he prays when he remembers it. [Al Mawsū`ah Al Fiqhiyyah Al Muyassarah p. 309].