It was narrated that 'Aishah said:
"If the Messenger of Allah (ﷺ) wanted to sleep while he was Junub, he would perform Wudu' as for prayer before sleeping." (RU)
English reference (RU): Vol. 1, Book 1, Hadith 259 (RU)
Arabic reference (RU): Book 1, Hadith 260 (RU)