Umarh bint 'Abdur Rahman عمرة بنت عبد الرحمن بن سعد بن زرارة · The Book of Purification and its Sunnah

"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.'"