It is narrated from Hazrat Aisha (may Allah be pleased with her) that when the Prophet (peace and blessings be upon him) wanted to sleep or eat something in a state requiring ghusl, he would perform ablution as for prayer.
Hadith Referenceمسند احمد / مسند النساء / 26383
Hadith Gradingحکم دارالسلام:حديث صحيح، وهذا إسناد ضعيف جدا لأجل عامر بن صالح