It is narrated from Hazrat Aisha that sometimes ghusl (ritual bath) would become obligatory upon the Prophet (peace be upon him), but the Prophet (peace be upon him) would sleep without touching water, then he would wake up and again sleep in the same way.
Hadith Referenceمسند احمد / مسند النساء / 24799
Hadith Gradingحکم دارالسلام:رجاله ثقات غير شريك، فهو ضعيف، راجع 24778