Now, let us see what the Quran, says about the Ahlul-Bait or the Family Members of The Holy Prophet.
According to the Quran, the following persons were sinless and infallible at the time of the death of the Holy Prophet: Ali, Fatimah, Hassan and Hussain.
The Ayat of 'Tat'heer' or Purity runs as follows:
"And Allah only wishes to keep all abomination away trom you,
O Members of the Family, and to keep you as pure and spotless most perfectly."
QURAN:: 33: 33
It is universally agreed that the above named four persons are definitely 'Members of the Family' and they are sinless and free from all kind of abomination.
The sentences before and after this Ayat are addressed to the wives of The Holy Prophet and the pronouns are of feminine gender: but the pronouns in this Ayat are of masculine gender. The reason why this Ayat has been placed in its present place is not difficult to guess.
The late renowned scholar Allama Poya writes in the footnote No. 1857 of the translation of the Holy Quran by S.V. Mir Ahmad Ali:
"The portion of this verse relating to the divinely effected purity of the Holy Ahlul-Bait needs a proper explanation commenting with reference to its correct context. This portion of this verse is a separate Ayat or verse by itself revealed separately on particular occasions but placed here as it deals with the wives of The Holy Prophet. The location of this verse here if studied properly makes it abvious that it has its own significant and important purpose behind it. While the address in the beginning of this verse is in the feminine gender - there is the transition here in the address from the feminine to the masculine gender. While referring to the consorts of The Holy Prophet, the pronouns also are consistently feminine. For a mixed assembly of men and women, generally the masculine gcnder is used. This transition in the grammatical use of the larguage, makes it luite obvious that this clause is quite a different matter used for a different group other than the previous one, and has been suitably placed here to show a comparative position of the Ahlul-Bait in contrast to the wives of The Holy Prophet. Amr Ibn Abi Salma who was brought up by The Holy Prophet relates:
"When this verse was revealed The Holy Prophet was in the house of Umme-Salema. At the revelation of:-
'Verily willeth God to keep away imputity from you, O People of the House and He purifieth you with the perfect purification,'
The Holy Prophet assembled his daughter Fatimah, her sons Hassan and Hussain and her husband, his cousin Ali. And covered the group including himself, with his own mantle and addressing God said,
'O God! These constitute my progeny! Keep them away from every kind of impurity, purified with perfezt purification.'
Umme-Salema, thc righteous wife of The Holy Prophet, witnessing this marvellous occasion, humbly submitted to the Holy Prophet 'O Apostle of God! May I also join the group?' to which the Holy Prophet replied,
'No, remain thou in thine own place, thou art in goodness'."
It is not the place to give the countless references concerning this Ayat; still, I would like to quote Maulana Wahiduzzaman, the famous Sunni Scholar, whose translation and comment of Quran as well as his book 'Anwarul-Lugha' (being the dictionary of Quran and Traditions) are among the recognized reference books. He writes in his commentary of Quran about this 'Ayat'- "Some people think that it is especially for those family members who had blood relations with the Prophet, i.e. Ali, Fatimah, Hassan and Hussain. The present translator, i.e. Himself, says that correct (Saheeh) and well connected upto Prophet (Merfuu) traditions support the same view, because when The Prophet himself has declared that my Family Members are only these, then to accept it and believe in it becomes obligatory. And one more sign of correctness of this view is that the pronouns used before and after this verse are those for females, while in this verse are those for males... " (Tafseer Wahidi, on the margin of the translation of Qurran, by the same author, printed at Gelani Press, Lahore, Para 22, Page 549, Footnote No. 7).
Again he says in his dictionary of Quran and Traditions (Anwarul-Lugha, Para 22, Paae 51): "The correct view is that in this Ayat of 'Purity' only these five persons are included (i.e. The Prophet, Ali, Fatimah, Hassan and Hussain), though in the usage of Arabs, the word 'Ahlul-Bait' is used for wives also. Some people prove by this Ayat that these five persons were sinless and Ma'soum (Infallible). But, if not 'Ma'soum', then of course, they were MAHFOUTH (Protected from committing any sin or error) surely."
I have quoted these two references (though I do not agree fully with him in some of his assertions) just to show that not only the Ithna'asheris but the learned men of Sunnis also confirm that, according to the rules of Arabic Grammer and according to the correct unbroken traditions of The Prophet only Ali, Fatimah, Hassan and Hussain are included in it besides The Prophet himself. Also it is clear that our claim that these persons were sinless, is shared by the Sunni scholars also. It is apparent that the least they say is that even if not infallible (theoratically) they were protected from sins and errors (practically).
There are many other Ayats and traditions testifying to the ISMAT or Purity of Ahlul-Bait. But the limitation of these pages does not allow me to enumerate them even briefly.