It is narrated from Sayyidah Aishah (may Allah be pleased with her): The Messenger of Allah (peace and blessings be upon him) and I used to bathe from a single vessel, and he (peace and blessings be upon him) would begin before me.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 895