It is narrated from Sayyidah Aishah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) used to bathe from a bowl of this size, and Abu Asim showed us the size of the bowl with his hand: it was a bowl that held eight ratls of water. Then he would pour water on the right side of his head, then on the left side of his head, then take a handful of water and pour it on the middle of his head.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 872