Ibn Abi al-Shuwarab محمد بن عبد الملك بن أبي الشوارب · The Book of Purification and its Sunnah

They all heard the Messenger of Allah say: 'Complete the ablution. Woe to the heels because of Hell-fire."

"The Messenger of Allah would fall asleep until he was breathing deeply, then he would get up and offer the prayer, and he did not perform ablution." (Hasan) Tanafisi said: "Waki` said: 'She meant while he was prostrating (he would sleep).'"