مِشْكَاةُ الْمَصَابِيحِ
Mishkat al-Masabih 2684
The Rites of Pilgrimage
What one who is in the Sacred State must avoid - Section 1
وَعَن أَبِي أَيُّوبَ: أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ كَانَ يَغْسِلُ رَأْسَهُ وَهُوَ مُحْرِمٌ
Abu Ayyub said that the Prophet (ﷺ) used to wash his head when he was in the sacred state. Bukhari and Muslim.
Mishkat al-Masabih, 2684مُتَّفق عَلَيْهِ (الألباني)