(a) It is narrated from Sayyidah Aishah (may Allah be pleased with her) that when the Messenger of Allah (peace and blessings be upon him) intended to sleep while in a state of janabah, he would perform an ablution like the ablution for prayer.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 966