The type of sleep that invalidates wuḍū is deep sleep in which the person is not aware of what state he is in. Light sleep does not invalidate wuḍū because the Ṣaḥābah (the Prophet’s (May Allāh praise him and Peace be upon him) Companions) would doze while waiting for prayer and would then stand up to pray without performing wuḍū`. [Ṣaḥīḥ Muslim: 376].