Sayyidah Aishah (may Allah be pleased with her) said: When the Messenger of Allah (peace and blessings be upon him) took the ritual bath for janabah, he would call for something like a large bowl, then take a handful of water and begin with the right side of his head, then the left side, then take water with both palms and pour it over his head.
(b) 'Al-hilab' means the vessel in which milk is drawn; it was called hilab.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 871
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