If you show the Salafi/wahabi a signed paper by the PROPHET (s) they will refuse, they are wrapped in the shackles of BANI UMMAYA!!!
In another Sunni commentary of Quran, it is narrated on the authority of Abdullah Ibn Umar that:
The Messenger of Allah (s) said: "Had there been any soul on the whole earth better than Ali, Fatimah, al-Hasan and al-Husain, Allah would have commanded me to take them along with me to Mubahala. But as they were superior in dignity and respect to all human be beings, Allah confined His choice on them only for participation in Mubahala."
Sunni reference: Tafsir al-Baidhawi, under the commentary of Verse 3:61
Concluding, the event of Mubahala between the Prophet (s) the Christians was significant in many aspects, among them are:
1. It proved to be a lesson for all the Christians of Arabia who no longer dared any confrontation with the Holy Prophet (s).
2. The invitation of "Mubahala" (literally meaning cursing each other) was directed by Allah and it was in compliance with His Command that the Holy Prophet and his Ahlul-Bayt along with him to the field of Mubahala. This serves to show how affairs pertaining to prophethood and Islam are determined by the Will of Allah; allowing no margin of interference from the common people (Ummah). (The matter of Imam Ali's (AS) succession after the Prophet should be viewed similarly)
3. The indispensability of Imam Ali, Lady Fatimah, Imam al-Hasan and Imam al-Husain in the following of the precepts of the Holy Prophet could no longer be disputed.
4. Notwithstanding their childhood, al-Hasan and al-Husain did nevertheless serve as two active partners of the Holy Prophet on the field of Mubahala. This yields the conclusion that age is no criteria for the greatness of those infallible souls.
5. That the Holy Prophet's act of having preferred a few obviously elevates their status above all others.
6. Traditions from the Prophet with regards to this event clearly indicates who the Ahlul-Bayt are.
7. Imam Ali (AS) has been mentioned as the 'Self' of the Prophet (s) according to the revelation of Allah, and is, in fact, superior to all others with regard to the matter of succession.
Is is not about Blood Relationship.
It is narrated that:
The Messenger of Allah said: "Any relation will end on the day of Judgment except my relation. And the root (identification) of every one is his father, except the progeny of Fatimah, since I am their father and their root (identification)."
Sunni references:
Ibn al-Jawzi, al-Bayhaqi, and al-Darqunti, al-Dhahabi on the authorities of Umar Ibn al-Khattab, Ibn Abbas, Ibn Zubair, and Ibn Umar.
al-Sawa'iq al-Muhriqah, by Ibn Hajar al-Haythami, Ch. 11, section 1, p239
Similar tradition has been narrated by Abu Ya'la, al-Tabarani on the authority of Fatimah (AS) and Ibn Umar.
The above precious tradition proves that, blood relationship is of little value in Islam and it will soon melt away when the day of Judgment appears. But what makes the relationship of the Prophet and his Ahlul-Bayt different than others is the qualifications and spiritual purity that they have besides their pure gene (which is also necessary).
For that reason, Allah revealed the Chapter of "al-Kawthar":
"Lo! We have given you Abundance (i.e., a long-standing pure progeny). So pray unto your Lord, and sacrifice. Lo! It is your insulter (and not you) who is without progeny." (Quran, Chapter 108).
In the above Chapter, Allah refers to Fatimah al-Zahra as Abundance who brings for the Prophet a sanctified progeny. Again, by progeny we do not mean all those whose ancestor are the Prophet (s). We rather mean those among his descendants who have been thoroughly purified by Allah, and the history and the Hadith can not count more that 14 of them (including the Prophet). Here is the commentary of the above Chapter by Yusuf Ali (the translator of Quran):
Abu Jahl and his Pagan confederates vented their personal spite and venom against the holy Prophet by taunting him with the loss of his two infant sons by Khadija, but where were these venomous detractors a few years afterwards, when the divine Light shone more brilliantly than ever?
Fatimah received severe injuries and was martyred at the age of eighteen, just six months after the demise of the Prophet, leaving two sons: al-Hasan, and al-Husain. After martyrdom of Imam Ali (AS), Imam al-Hasan came to power. But Muawiyah, the disloyal governor of Syria, continued his aggression by preparing another attack (after the war of Siffin), and meanwhile he bought the key elements of the army of Imam al-Hasan by money and bribe, and by corrupting his army, was finally able to complete a peaceful military coup, and to take over the power. Imam al-Hasan was poisoned to death shortly after.
The second (and the last) grandson of the Prophet was Imam al-Husain (AS), who was slaughtered along with his family (except one of his sons), relatives, and companions, in the desert of Karbala, by the army of Yazid, the corrupt and drunk son of Muawiyah. That catastrophe took place only 50 years after the demise of the Prophet!!!
The above was a very short horrible story of what happened to Ahlul-Bayt, whom Quran and the Prophet (s) ordered us to love them and obey them beside the book of Allah.