Hadith no. 2304 (below) is a repeat. Read it here.
Volume 3, Book 48, Number 806 :
Narrated by Abdullah bin Umar (radiallaahu `anhu)
Allah’s Apostle (sallallaahu `alayhi wasallam) and Ubai bin Kab Al-Ansari (radiallaahu `anhu) went to the garden where Ibn Saiyad used to live. When Allah’s Apostle (sallallaahu `alayhi wasallam) entered (the garden), he (i.e. Allah’s Apostle) started hiding himself behind the datepalms as he wanted to hear secretly the talk of Ibn Saiyad before the latter saw him. Ibn Saiyad wrapped with a soft decorated sheet was lying on his bed murmuring. Ibn Saiyad’s mother saw the Prophet (sallallaahu `alayhi wasallam) hiding behind the stems of the date-palms. She addressed Ibn Saiyad saying, “O Saf, this is Muhammad.” Hearing that Ibn Saiyad stopped murmuring (or got cautious), the Prophet (sallallaahu `alayhi wasallam) said, “If she had left him undisturbed, he would have revealed his reality.”
Volume 3, Book 48, Number 807 :
Narrated by Aisha (radiallaahu `anhaa)
The wife of Rifa’a Al-Qurazi came to the Prophet (sallallaahu `alayhi wasallam) 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 (sallallaahu `alayhi wasallam) asked her ‘Do you want to remarry Rifa’a? You cannot unless you had a complete sexual relation with your present husband.” Abu Bakr (radiallaahu `anhu) was sitting with Allah’s Apostle (sallallaahu `alayhi wasallam) and Khalid bin Said bin Al-‘As (radiallaahu `anhu) 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 (sallallaahu `alayhi wasallam)?”
If a man divorces his wife with the first or second talaaq, once her ‘iddah is over she is divorced and becomes a “stranger” (non-mahram) to him; she cannot go back to him except with a new marriage contract which fulfills all the conditions set out in sharee’ah.
But if he divorces his wife with the third talaaq, then she becomes haraam to her first husband until she has married a second husband in a genuine marriage which is consummated. The Qur’aanic evidence for that is the aayah (interpretation of the meaning):
“The divorce is twice, after that, either you retain her on reasonable terms or release her with kindness…
And if he has divorced her (the third time), then she is not lawful unto him thereafter until she has married another husband”
The last divorce refers to the third divorce, according to all the scholars.
The evidence from the Sunnah is the hadeeth narrated by ‘Urwah ibn al-Zubayr, according to which ‘Aa’ishah told him that the wife of Rifaa’ah al-Qurazi came to the Messenger of Allaah (peace and blessings of Allaah be upon him) and said, “O Messenger of Allaah, Rifaa’ah divorced me thrice, then I was married to ‘Abd al-Rahmaan ibn al-Zubayr al-Qurazi, but he has nothing with him except something like this fringe. The Messenger of Allaah (peace and blessings of Allaah be upon him) said, “Perhaps you want to go back to Rifaa’ah? No, (it is not possible), unless and until you enjoy the sexual relation with him (‘Abd al-Rahmaan), and he enjoys the sexual relation with you.”
(Narrated by al-Bukhaari, 4856; Muslim, 2587)
The phrase “divorced me three times” means that this was the divorce which meant that she was no longer married to him, which is the third talaaq. The Prophet’s words “until you enjoy the sexual relation with him (‘Abd al-Rahmaan), and he enjoys the sexual relation with you” refer to intercourse.
Al-Nawawi said: “This hadeeth indicates that the woman who has been divorced by a third talaaq is not permissible to the man who has divorced her until she has been married by another husband, who has intercourse with her then separates from her, and she completes her ‘iddah. Merely drawing up the marriage contract with her does not make her permissible to the first husband. This is the view of all the scholars among the Sahaabah, Taabi’een and those who came after them.
Sharh Muslim, 10/3
Taken from IslamQA