Sahih al-Bukhari 1840
Sahih‘Abdullāh ibn ‘Abbās and Al-Miswar ibn Makhramah (may Allah be pleased with both of them) were at Al-Abwā' when they disagreed over a matter. Ibn ‘Abbās said: "The one in the state of Ihrām may wash his head." Al-Miswar said: "He may not wash his head." Ibn ‘Abbās sent me (the narrator) to Abu Ayyūb al-Ansāri (may Allah be pleased with him) to ask him about that. I found him taking a ritual bath between the two posts of a well, screened with a cloth. I greeted him and he said: "Who is that?" I replied: "‘Abdullāh ibn Hunayn. ‘Abdullāh ibn ‘Abbās sent me to ask you how the Messenger of Allah (may Allah's peace and blessings be upon him) used to wash his head while in the state of Ihrām. Abu Ayyūb put his hand on the cloth and lowered it until I could see his head, then he said to the person who was pouring out the water for him: 'Pour', and he poured some over his head. He passed his hands over his head from back to front then from front to back and said: "I saw the Messenger of Allah (may Allah's peace and blessings be upon him) washing it like this." Another narration adds: So Al-Miswar said to Ibn ‘Abbās: "I will never argue with you again."