Sayyiduna Abu Hurayrah (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "Under every hair there is janabah, so wet the hair and cleanse the skin thoroughly."
(b) Al-Harith bin Wajih alone narrated it in this way, and Yahya bin Ma'in (may Allah have mercy on him) said about al-Harith bin Wajih: His hadith is worth nothing.
(c) Among the scholars of hadith, Imam al-Bukhari (may Allah have mercy on him), Imam Abu Dawud (may Allah have mercy on him) and others have rejected it. Al-Hasan al-Basri (may Allah have mercy on him) narrates it from the Prophet (peace and blessings be upon him) as a mursal report, and likewise Imam al-Hasan al-Basri narrates it from Sayyiduna Abu Hurayrah (may Allah be pleased with him) as a mawquf report, and something similar is transmitted from Imam al-Nakha'i (may Allah have mercy on him).
(d) Imam al-Shafi'i (may Allah have mercy on him) interpreted it as referring to what is outward; the inside of the nose and mouth are among the hidden parts, so they resemble the inside of the eyes and the inside of the ears. The one who debated this issue with Imam al-Shafi'i (may Allah have mercy on him) said: Analogy requires that he does not repeat (the bath), but we have taken the report from Sayyiduna Ibn Abbas (may Allah be pleased with them both).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 849