one narration:

“Whoever sleeps, let him perform ablution.”

This is also supported by the report in the two Sahīh collections that the Prophet:

“Would sleep until he was breathing heavily, then rise and pray without performing ablution.”

This was because his eyes would sleep but his heart would not; he remained aware. Had anything passed from him, he would have felt it. This shows that sleep is not itself a state of ritual impurity. If it were, there would be no distinction in this regard between the Prophet and anyone else, just as there is none regarding urination, defecation, and other causes of ritual impurity.

It is also established in the Sahīh collection that the Prophet:

“Would delay the night prayer until the Companions of Allah’s Messenger were nodding their heads; then they would pray without performing ablution.”

This shows that sleep as such does not invalidate ablution. If it did, their ablution would have been invalidated by this sleep in which their heads nodded.

Beyond this, scholars hold three views:

One view is that sleep in any position other than sitting invalidates ablution, without qualification. This is the view of Mālik and one view reported from Ahmad.

Another view is that sleeping while standing or sitting does not invalidate ablution, whereas sleeping while bowing or prostrating does;