Sayyidah Aishah (may Allah be pleased with her) said that when the Messenger of Allah (peace and blessings be upon him) was in a state of janabah and he (peace and blessings be upon him) intended to sleep or eat, he would perform ablution.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 976