Sahih Bukhari Volume 007, Book 063, Hadith Number 262.
Narrated By Ibn 'Umar : The Prophet said to those who were involved in a case of Lian, "Your accounts are with Allah. One of you two is a liar. You (husband) have right on her (wife)." The husband said, "My money, O Allah's Apostle!" The Prophet said, "You are not entitled to take back any money. If you have told the truth, the Mahr that you paid, was for having sexual relations with her lawfully; and if you are a liar, then you are less entitled to get it back."