Musannaf Ibn Abi Shayba 1:150

Abu Bakr narrated to us, he said: Hafs ibn Ghiyath narrated to us, from Layth, from Talha, from his father, from his grandfather, who said: I saw the Prophet, may Allah bless him and grant him peace, perform ablution (wudu), and he wiped his head like this. And Hafs moved his hands over his head until he wiped the back of his neck.