It is narrated from Sayyidah Aisha (may Allah be pleased with her) that when the Prophet Muhammad (peace and blessings be upon him) intended to eat something or sleep while in a state of major ritual impurity (janabah), he would perform ablution (wudu).
Hadith Referenceصحيح ابن خزيمه / جماع أبواب فضول التطهير والاستحباب من غير إيجاب / 215