Bulugh al-Maram, Book 1, Hadith 134 (English)

Narrated Abu Hurairah (RAA): Allah's Messenger (Peace be upon him) said: "There is Janabah (trace of sexual impurity) under every hair, so wash your hair and cleanse the skin." Abu Dawud and at-Tirmidhi transmitted it but they declared it to be weak.

وَعَنْ أَبِي هُرَيْرَةَ ‏- رضى الله عنه ‏- قَالَ: قَالَ رَسُولُ اَللَّهِ ‏- صلى الله عليه وسلم ‏-{ إِنَّ تَحْتَ كُلِّ شَعْرَةٍ جَنَابَةً, فَاغْسِلُوا اَلشَّعْرَ, وَأَنْقُوا اَلْبَشَرَ } رَوَاهُ أَبُو دَاوُدَ, وَاَلتِّرْمِذِيُّ وَضَعَّفَاه ُ (151)‏.‏ ‏5 ‏- منكر.‏ رواه أبو داود (248)‏، والترمذي (106)‏.‏

sunnah.com

also referenced under: Book 1, Hadith 152 (In-Book)

Ahmad transmitted a similar narration to the above, on the authority of `A'ishah (RAA), but this version has an unknown transmitter.

وَلِأَحْمَدَ عَنْ عَائِشَةَ نَحْوُهُ, وَفِيهِ رَاوٍ مَجْهُول ٌ (152)‏.‏ ‏6 ‏- ضعيف.‏ رواه أحمد (654)‏.‏

sunnah.com

also referenced under: Book 1, Hadith 153 (In-Book)