Muwatta Malik, Book 2, Hadith 41 (In-Book)

Yahya related to me from Malik from Nafithat Ibn Umar used to sleep sitting and then would pray without doing wudu.

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، أَنَّ ابْنَ عُمَرَ، كَانَ يَنَامُ جَالِسًا ثُمَّ يُصَلِّي وَلاَ يَتَوَضَّأُ ‏.‏

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also referenced under: Book 2, Hadith 10 (USC-MSA)