Sunan Abi Dawud 1840
‘Abd Allah bin Hunain said ‘Abd Allah bin Abbas and Miswar bin Makhramah differed amongst themselves (on the question of washing the head in the sacred state) at al Abwa. ‘Ibn Abbas said A pilgrim in the sacred state (while wearing ihram) can wash his head. Al Miswar said A pilgrim in the sacred state(wearing ihram) cannot wash his head. ‘Abd Allah bin Abbas then sent him (‘Abd Allah bin Hunain) to Abu Ayyub Al Ansari. He found him taking a bath between two woods erected at the edge of the well and he was hiding himself with a cloth (curtain). He (the narrator) said I saluted him. He asked Who is this? I said I am ‘Abd Allah bin Hunain. ‘Abd Allah bin Abbas has sent me to you asking you how the Apostle of Allaah(ﷺ) used to wash his head while he was wearing ihram. Abu Ayyub then put his hand on the cloth and removed it till his head appeared to me. He then said to a person who was pouring water on him:
Pour water. He poured water on his head and Abu Ayyub moved his head with his hands. He carried his hands forward and backward. 
He then said I saw him doing similarly.
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، عَنْ مَالِكٍ، عَنْ زَيْدِ بْنِ أَسْلَمَ، عَنْ إِبْرَاهِيمَ بْنِ عَبْدِ اللَّهِ بْنِ حُنَيْنٍ، عَنْ أَبِيهِ، أَنَّ عَبْدَ اللَّهِ بْنَ عَبَّاسٍ، وَالْمِسْوَرَ بْنَ مَخْرَمَةَ، اخْتَلَفَا بِالأَبْوَاءِ فَقَالَ ابْنُ عَبَّاسٍ يَغْسِلُ الْمُحْرِمُ رَأْسَهُ وَقَالَ الْمِسْوَرُ لاَ يَغْسِلُ الْمُحْرِمُ رَأْسَهُ فَأَرْسَلَهُ عَبْدُ اللَّهِ بْنُ عَبَّاسٍ إِلَى أَبِي أَيُّوبَ الأَنْصَارِيِّ فَوَجَدَهُ يَغْتَسِلُ بَيْنَ الْقَرْنَيْنِ وَهُوَ يُسْتَرُ بِثَوْبٍ قَالَ فَسَلَّمْتُ عَلَيْهِ فَقَالَ مَنْ هَذَا قُلْتُ أَنَا عَبْدُ اللَّهِ بْنُ حُنَيْنٍ أَرْسَلَنِي إِلَيْكَ عَبْدُ اللَّهِ بْنُ عَبَّاسٍ أَسْأَلُكَ كَيْفَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَغْسِلُ رَأْسَهُ وَهُوَ مُحْرِمٌ قَالَ فَوَضَعَ أَبُو أَيُّوبَ يَدَهُ عَلَى الثَّوْبِ فَطَأْطَأَهُ حَتَّى بَدَا لِي رَأْسُهُ ثُمَّ قَالَ لإِنْسَانٍ يَصُبُّ عَلَيْهِ اصْبُبْ ‏.‏ قَالَ فَصَبَّ عَلَى رَأْسِهِ ثُمَّ حَرَّكَ أَبُو أَيُّوبَ رَأْسَهُ بِيَدَيْهِ فَأَقْبَلَ بِهِمَا وَأَدْبَرَ ثُمَّ قَالَ هَكَذَا رَأَيْتُهُ يَفْعَلُ صلى الله عليه وسلم ‏.‏