On the authority of Ibn ʿUmar, who said: The prayer was fifty [in number], the washing from major ritual impurity was seven times, and the washing of urine from the garment was seven times. The Messenger of Allah, peace and blessings be upon him, kept asking until the prayer was made five, the washing from major ritual impurity once, and the washing of urine from the garment once. (1)

248 — Narrated to us Naṣr ibn ʿAlī: narrated to me al-Ḥārith ibn Wajīh: narrated to us Mālik ibn Dīnār, on the authority of Muḥammad ibn Sīrīn, on the authority of Abū Hurayrah, who said: The Messenger of Allah, peace and blessings be upon him, said: "Verily, beneath every hair there is a state of major ritual impurity, so wash the hair and cleanse the skin." (2)

Abū Dāwūd said: Al-Ḥārith's hadith is rejected (munkar), and he is weak.

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(1) Its chain of transmission is weak due to the weakness of Ayyūb ibn Jābir — he is Ibn Sayyār al-Ḥanafī al-Yamāmī — while ʿAbd Allāh ibn ʿIṣm — or ʿIṣmah — is truthful with good hadiths.
It was also narrated by Aḥmad (5884) and al-Bayhaqī 1/179 and 244–245 via two paths from Ayyūb ibn Jābir, with this chain.
That the prayer was made five after having been fifty has supporting witnesses, including the hadith of Mālik ibn Ṣaʿṣaʿah in al-Bukhārī (3207) and Muslim (164).
And the hadith of Abū Dharr in al-Bukhārī (349) and Muslim (163).
And the hadith of Anas in Muslim (162).

(2) Its chain of transmission is weak due to the weakness of al-Ḥārith ibn Wajīh, and the compiler declared him weak because of it.
It was also narrated by al-Tirmidhī (106) and Ibn Mājah (597) via the path of al-Ḥārith ibn Wajīh, with this chain. Al-Tirmidhī said: The hadith of al-Ḥārith ibn Wajīh is a strange (gharīb) hadith; we do not know it except from his narration.
His saying "beneath every hair there is a state of major ritual impurity" has supporting witnesses, but all of them are not free from criticism. Among them is the hadith of Abū Ayyūb al-Anṣārī in Ibn Mājah (598), and its chain is disconnected.
And among them is the hadith of ʿĀʾishah in Aḥmad (24797), and its chain is weak.
And among them is the hadith of ʿAlī, which follows after this one.