The Messenger of Allah ﷺ said, "Beneath every hair lies impurity, so wash the hair and cleanse the skin."
حدثنا نصر بن علي الجهضمي حدثنا الحارث بن وجيه حدثنا مالك بن دينار عن محمد بن سيرين
قال رسول الله ﷺ إن تحت كل شعرة جنابة فاغسلوا الشعر وأنقوا البشرة
Its isnad is daif. Reported by Abu Dawud, Chapter on Purification, section on ghusl from janaba, no. 248, and Tirmidhi, no. 106, who said, "The hadith of Harith bin Wajih is a gharib hadith, we do not know it except through his narration, and he is a shaikh who is not held in high regard."