Mishkat al-Masabih
Abu Ayyub said that the Prophet (ﷺ) used to wash his head when he was in the sacred state. Bukhari and Muslim.
وَعَن أَبِي أَيُّوبَ: أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ كَانَ يَغْسِلُ رَأْسَهُ وَهُوَ مُحْرِمٌ
Reference