Narrated `Aisha: Whenever the Prophet intended to sleep while he was Junub, he used to wash his private parts and perform ablution like that for the prayer.
Hadith ReferenceSahih Bukhari / The Book of Ghusl (Washing of the Whole Body) / Hadith: 288
Hadith Gradingمحدثین:أحاديث صحيح البخاريّ كلّها صحيحة