Hadith: How did the Messenger of Allah (may Allah's peace and blessings be upon him) wash his head when he was in the state of Ihrām?

عن عبد الله بن حنين أن عبد الله بن عباس رضي الله عنهما ، وَالْمِسْوَرِ بْنِ مَخْرَمَةَ رضي الله عنهما اختلفا بِالْأَبْوَاءِ: فقال ابن عباس: يغسل الْمُحْرِمُ رأسه. وقال الْمِسْوَر: لا يغسل رأسه. قال: فأرسلني ابن عباس إلى أبي أيوب الأنصاري رضي الله عنه فوَجَدْتُهُ يغتسل بين الْقَرْنَيْنِ، وهو يستر بثوب، فَسَلَّمْتُ عليه، فقال: من هذا؟ فقلت: أنا عبد الله بن حُنَيْنٍ، أرسلني إليك ابن عباس، يسألك: كيف كان رسول الله صلى الله عليه وسلم يغسل رأسه وهو مُحرِمٌ؟ فوضع أبو أيوب يده على الثوب، فَطَأْطَأَهُ، حتى بَدَا لي رأسه، ثم قال لإنسان يَصُبُّ عليه الماء: اصْبُبْ، فَصَبَّ على رأسه، ثم حَرَّكَ رأسه بيديه، فأقبل بهما وَأَدْبَرَ. ثم قال: هكذا رأيته صلى الله عليه وسلم يغتسل». وفي رواية: «فقال المسور لابن عباس: لَا أُمَارِيكَ أبدًا».
[صحيح] - [متفق عليه]

‘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."
Sahih/Authentic. - [Al-Bukhari and Muslim]

Explanation

‘Abdullāh ibn ‘Abbās and Al-Miswar ibn Makhramah (may Allah be pleased with both of them) were debating whether the one in the state of Ihrām is allowed to wash his head or not. What made it debatable is that if one moves the hair on his head, it may cause some of the hair to fall. So ‘Abdullāh ibn Hunayn went to Abu Ayyūb and found him washing himself. He said to Abu Ayyūb: Ibn ‘Abbās sent me to ask you how the Messenger of Allah (may Allah's peace and blessings be upon him) used to wash himself (while in Ihrām). Abu Ayyūb said to the one who was pouring the water for him: "Pour," after he had lowered the cloth that was screening him until his head was visible, then he moved his hair with his hands, going from back to front and from front to back. Then he said: "This is what I saw the Messenger of Allah (may Allah's peace and blessings be upon him) doing." When ‘Abdullāh ibn Hunayn informed them (Ibn ‘Abbās and Al-Miswar) that ‘Abdullāh ibn ‘Abbās was right - as the Companions always sought to know what the correct thing to do is- Al-Miswar (may Allah be pleased with him) recanted and admitted the virtue of his companion, saying: "I will never argue with you again."