Is it true that the Wudu of the Prophet, sallallaahu alayhi wa sallam, would not get nullified even if he slept? This is what I heard in a lecture by the Tableeghi Jamaat's Aalim (Tariq Jameel).

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

What you have heard about the ablution of the Prophet that it is not invalidated by him being asleep is correct. Indeed the Prophet said: "My eyes sleep but my heart does not." [Al-Bukhari] Moreover, Ibn 'Abbaas narrated that The Prophet slept until he was snoring and then he woke up and prayed without performing ablution. Imaam An-Nawawi said in his interpretation of the narrations: 'This is peculiar to the Prophet that his sleeping lying down does not invalidate his ablution because his eyes sleep while his heart is awake, so if he passes any gas he would have felt it, unlike other people.'

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Allaah Knows best.