´It was narrated that 'Ali said:` "A man came to the Prophet and said: 'I bathed to cleanse myself from sexual impurity, and I prayed Fajr, then I noticed a spot the size of a fingernail that the water did not reach.' The Messenger of Allah said: 'If you had wiped it that would have been sufficient for you.'"
Explanation & Benefits
Maulana Ataullah Sajid
Commentary:
Both of these narrations are weak; therefore, the issue mentioned in them is not established from them.
Thus, in such a situation, repeating the ritual bath (ghusl) or ablution (wudu) would be necessary.
And Allah knows best.
Source: Commentary on Sunan Ibn Mājah by Mawlānā ‘Atā’ullāh Sājid, Page: 664