Musannaf Ibn Abi Shayba 1:1066

Ghundar narrated to us, from Shu'bah, from 'Amr ibn Murrah, from Abu al-Bakhtari, who said: Hudhayfah went out, and he had gathered his hair. He said: "Indeed, under every hair that the water does not reach is a state of major ritual impurity (janabah), so avoid them. That is why I have treated my head as you see."