Mishkat al-Masabih 10 The Rites of Pilgrimage كتاب المناسك 174

وَعَن أَبِي أَيُّوبَ: أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ كَانَ يَغْسِلُ رَأْسَهُ وَهُوَ مُحْرِمٌ

Abu Ayyub said that the Prophet used to wash his head when he was in the sacred state. Bukhari and Muslim.