مُوَطَّأُ مَالِكٍ
Muwatta Malik 41
Purity
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، أَنَّ ابْنَ عُمَرَ، كَانَ يَنَامُ جَالِسًا ثُمَّ يُصَلِّي وَلاَ يَتَوَضَّأُ .
Yahya related to me from Malik from Nafithat Ibn Umar used to sleep sitting and then would pray without doing wudu.
Arabic/English book reference: Book 2, Hadith 10