Muwatta Imam Malik Book of Purity, Hadith 11b

Yahya related to me from Malik from Nafi that 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 وَلَا يَتَوَضَّأُ»