Quiz of the day – Question

When any one of you sleeps deeply and wakes up for prayer it has been instructed by rasoolullah sallallahu alaihi wasallam that he has to perform Wudhu.

But in the case of Rasoolullah sallallahu alaihi wasallam he used to sleep deeply with snoring and when he woke up he did not perform Wudhu and prayed directly?

Can you explain why this exception?