Abu Dawud Book 33, Hadith Number 4452.

Narated By Abdullah ibn Abbas : A man of Bakr ibn Layth came to the Prophet (PBUH) and made confession four times that he had committed fornication with a woman, so he had a hundred lashes administered to him. The man had not been married. He then asked him to produce proof against the woman, and she said: I swear by Allah, Apostle of Allah, that he has lied. Then he was given the punishment of eighty lashes of falsehood.