The passing of wet hands over the head once only (while performing ablution)

Narrated `Amr bin Yahya: My father said, "I saw `Amr bin Abi Hasan asking `Abdullah bin Zaid about the ablution of the Prophet. `Abdullah bin Zaid asked for an earthenware pot containing water and performed ablution in front of them. He poured water over his hands and washed them thrice. Then he put his (right) hand in the pot and rinsed his mouth and washed his nose by putting water in it and then blowing it out thrice with three handfuls of water Again he put his hand in the water and washed his face thrice. After that he put his hand in the pot and washed his forearms up to the elbows twice and then again put his hand in the water and passed wet hands over his head by bringing them to the front and then to the back and once more he put his hand in the pot and washed his feet (up to the ankles.)"