Abdullah bin Hunayn (may Allah have mercy on him) says: Ibn Abbas (may Allah be pleased with them both) and Miswar bin Makhramah (may Allah be pleased with him) differed about the muhrim washing his head, so they sent me to Abu Ayyub al-Ansari (may Allah be pleased with him). I came to him while he was bathing between the two posts of a well. When he saw me, he drew the cloth to himself. I said: Your nephew Ibn Abbas (may Allah be pleased with them both) has sent me to you to ask you: How did you see the Messenger of Allah (peace and blessings be upon him) pouring water over his head while he was in the state of ihram? So he poured water over his head and said: Like this; and he placed his hands on his head and moved them from front to back three times.
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 3962