I tied my hair into tight braids, and the Prophet ﷺ said, "Ayesha, do you not know that beneath every hair there is impurity from janabah?"
حدثنا أسود بن عامر قال حدثنا شريك عن خصيف قال حدثني رجل منذ ستين سنة
أجمرت رأسي إجمارا شديدا فقال النبي ﷺ يا عائشة أما علمت أن على كل شعرة جنابة
Its chain of transmission is daif, due to the anonymity of the narrator from Ayesha. The hadith "Under every hair is a state of ritual impurity" was narrated by Abdul-Razzaq (1/262, no. 1002) from Hasan as a mursal report. Also by Bayhaqi (1/175) and Abu Naeem in al-Hilyah (2/388). See the comments of Ibn Hajar on it in Talkhis al-Habir (1/142).