وَعَن أَبِي أَيُّوبَ
أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ كَانَ يَغْسِلُ رَأْسَهُ وَهُوَ مُحْرِمٌ
The Prophet (sallallahu alayhi wa sallam) used to wash his head when he was in the sacred state. Bukhari and Muslim.
Mishkat al-Masabih 2572, Book 11, The Rites of Pilgrimage, Hadith 174. 1 min read