Because when the eyes of the Prophet ( صلی اللہ علیہ وسلم ) sleep, his heart remains awake. In the same way, there is a difference between the Prophet ( صلی اللہ علیہ وسلم ) and the Ummah regarding the obligation of ablution after sleep. For the Ummah, ablution becomes obligatory after sleep, but not for the Prophet ( صلی اللہ علیہ وسلم ).

It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) said: "My eyes sleep but my heart does not sleep."