Sahih Bukhari Volume 003, Book 048, Hadith Number 807.
Narated By 'Aisha : The wife of Rifa'a Al-Qurazi came to the Prophet and said, "I was Rifa'a's wife, but he divorced me and it was a final irrevocable divorce. Then I married AbdurRahman bin Az-Zubair but he is impotent." The Prophet asked her 'Do you want to remarry Rifa'a? You cannot unless you had a complete sexual relation with your present husband." Abu Bakr was sitting with Allah's Apostle and Khalid bin Said bin Al-'As was at the door waiting to be admitted. He said, "O Abu Bakr! Do you hear what this (woman) is revealing frankly before the Prophet ?"