In fact...
In fact, this is an undisputable fact, which both Shiite and Sunni scholars unanimously agree. Among the sayings of Sunni scholars who reported narrations to this effect are: Masrouq reports that Aisha told him: "We, the Prophet's wives, were gathered around him when Fatima walked towards us; by Allah her walk is exactly the same as that of the Messenger of Allah when he saw her, he greeted her by saying: `Welcome my daughter.' He then asked her to sit to his right or left.
He then whispered something to her that caused her to cry; when he saw her sadness, he whispered something else to her which caused her to laugh.
(When I saw this) I said to her: `The Messenger of Allah bestowed you with a special secret, yet you cry?' When the Prophet (S) left I exclaimed: "What did he whisper to you?" Fatima az-Zahra (sa) answered: `I would not announce the secret of the Messenger of Allah!' After the Prophet's (as) death, I said to her: `I insist on you-by my right over you-to tell me (what he told you)!' She (Fatima az-Zahra (sa)) said: 'Yes, I will tell you now.
The first time he whispered to me, he told me that Gabriel used to review the Qur’an with him once a year, but this year he reviewed it twice. So, he said, I think the time of my departure is near. Therefore, fear Allah and be patient, for I will be a good (person) to proceed you.' Fatima added: `so I cried, as you saw.
When he noticed my sadness, he once again said to me: 'Fatima, is it not satisfying to you to be theMistress of believing women (or the Mistress of the women of my Ummah)?" Baghawi in his book Masabeh As-Sunna writes that the Prophet (S) said to Fatima az-Zahra (sa): "Is it not satisfying to you to be the Mistress of the women of the world?" Hakim Nishabouri reported in his book Mustadrakthat he said to Fatima az-Zahra (sa): "Is it not satisfying to you to be the Mistress of the women of the world, this Ummah and believing women?" Although there are a large number of narrations, which state that Fatima az-Zahra (sa) was “the Mistress of all women”.
Ahmad Ibn Hanbal mentions at the end of the first narration that he also informed Fatima az-Zahra (sa) that she was the first one to follow him after his death. Bukhari reported in v.5, p.21 and 29 of his Sahih that Allah's Messenger (as) said: "Fatima is part of me, he who harms her harms me." This narration has been reported with a variety of words which all have the same meaning; it has been reported by more than fifty narrators.