Sunan Ibn Majah Book 1, Hadith 210

"He would sleep like that while he was sitting up."

Previous Hadith

The Messenger of Allah slept until he was breathing deeply, then he got up and prayed.

Sunan Ibn Majah Book 1, Hadith 209
Next Hadith

The Messenger of Allah said: "The eye is the leather strap (that ties up) the anus, so whoever falls asleep, let him perform ablution."

Sunan Ibn Majah Book 1, Hadith 211