Sayyidah Aishah (may Allah be pleased with her) says: When the Messenger of Allah (peace and blessings be upon him) took the ritual bath for janabah (major impurity), he would begin by washing his palms three times, then perform ablution as for prayer, then put his hand into the vessel and run it through the roots of his hair, until I was sure that he (peace and blessings be upon him) had reached the skin. Then he would pour water over his head, and then pour water over the rest of his body.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 813