It was narrated that `A'ishah said:
"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).'"
English reference: Vol. 1, Book 1, Hadith 474
Arabic reference: Book 1, Hadith 512