Sahih al-Bukhari 1840

Narrated `Abdullah bin Hunain:`Abdullah bin Al-Abbas and Al-Miswar bin Makhrama differed at Al-Abwa'; Ibn `Abbas said that a Muhrim could wash his head; while Al-Miswar maintained that he should not do so. `Abdullah bin `Abbas sent me to Abu Aiyub Al-Ansari and I found him bathing between the two wooden posts (of the well) and was screened with a sheet of cloth. I greeted him and he asked who I was. I replied, "I am `Abdullah bin Hunain and I have been sent to you by Ibn `Abbas to ask you how Allah's Messenger (ﷺ) used to wash his head while in the state of Ihram." Abu Aiyub Al-Ansari caught hold of the sheet of cloth and lowered it till his head appeared before me, and then told somebody to pour water on his head. He poured water on his head, and he (Abu Aiyub) rubbed his head with his hands by bringing them from back to front and from front to back and said, "I saw the Prophet (ﷺ) doing like this