Who are Ahlulbayt?

The Ahlal Bait are the Godly ones of the Family of the Holy Prophet whom the Muslim World as a whole unanimously acknowledges as the Pure Personalities and hold them as INFALLIBLE Holy ones PURIFIED By God Himself. 

* The Almighty Allah has bestowed His trust on Ale Muhammad (The descendants of Muhammad, Peace Be Upon Them), who are the Strongholds of His Commandments. From where they are expounded and interpreted. They are The Fountain Heads of Knowledge Created by Him, Shelters for His Teachings, Forts for Heavenly Books, And lofty Citadels to defend His Religion. Islam needed help and support, By them Allah made Islam strong and powerful.* 

"And We assigned from among them some Imams(Leaders) who guide by Our Authority since they were patient and believed firmly in Our Signs. (Qur'an 32:24)

And, He it is who made the stars for you that ye maybe rightly guided by observing them in the darkness of the land and the sea; Indeed we have made plain the Signs for the people who can know. (Qur'an 6:97).

The Ahlul Bayt or household of the Prophet Muhammad - peace be upon him and his household [pbuh] - refers to his daughter Fatima al-Zahra, his successor and son-in-law, Imam Ali, their two sons Imam Hasan and Imam Husayn, and the nine Imams from the lineage of Imam Husayn, peace be upon them all. 

 The Holy Prophet said: 

" As the stars in the sky are the Source of guidance to the travellers, The Holy Ones of my Ahlal Bait ( The Twelve Imams) are The Source of Guidance for the people. And, as the stars will remain in the sky until The Day of Judgment, The earth will never be without a Divinely Guide from My Ahlal Bait, That is an Imam". 

And say those who disbelieve: "why hath not a sign been sent down unto him(Muhammad); Verily thou art a Warner and for every people there is a guide (13:7)

Firmly Ground in Knowledge: 

"He (God) is He Who Has revealed The Book (Quran) to you. Some of its verses are decisive; they are the Essence of The Book and the others are ambiguous; so as for those in whose hearts there is perversity, they follow the part of it which is ambiguous, seeking to mislead (people) and seeking to give it ( their own) interpretation. But NONE knows its interpretation , Save God and those who are firmly established in Knowledge".(Qur'an 3:7). 

"Nay These are The Verses of The Qur'an in the Breast of those who are gifted with Knowledge. (Qur'an: 29:49).

The Blessed Ones: 

Guide us in the straight path: The path of those whom Thou hast blessed. (1:6&7). 

They are those whom Allah has blessed among the Prophets and the truthfuls, and the martyrs and the righteous. (4:69) 

These are The Ones on The Guidance from their Lord and these are The Ones shall be The successful ones. (Qur'an: 2:5).

 The Purified Ones: 

Verily It is Qur'an honourable,In a Book hidden, Toucheth It not save the purified ones. Sent down by The Lord of the Worlds. (56:77 to 80). 

The Highest degree of purity means to be kept constantly away from all the causes of impurity. This is termed as the State of Infallibility in Knowledge, character and action. It could have been applied generally to the whole mankind who are keeping aloof from all the impurities as The Word of God Commands; But, God expressively Has confined His Order to certain Group of Individuals by excluding the rest of the mankind from it in His Divine Will by declaring the 'Ahlal Bait' as the persons purified by Him to be constantly in touch with the Qur'an in its original, hidden, well protected, exalted and purified form. It was Allah's Wish to remove all Blemish from them: 

Verily, verily God intendeth to keep off from you (every kind of filth), "O' ye The People of The House (Ahlul Bait), and purify you with a thorough purification. (Qur'an: 33:33).

Commandment to love Ahlal Bait  In this Last Word of God (Qur'an), The Holy Prophet is being Commanded to ask the believers to love his kith and kin (that is his Ahlal Bait) and that would be the return of his apostleship. 

 That is of which God Give the glad tidings unto His servants who believe and do good deeds; Say thou ('O' Apostle Muhammad!) " I demand not of you any recompense for it (the toils of apostleship) save THE LOVE OF (MY) RELATIVES...(42:23).

Therefore, based on the above and other lines of evidence, it is the belief of Islam that the Holy Prophet and his family [peace be upon them] were blessed by Allah and purified to the level of being pure and sinless throughout their distinguished lives.and those who dont believe Ahl-ul-bayt as purified ones are out of the
of the main stream of Islam because they are against the Quran and sayings of Prophet Muhammad(s.a.w.s)

From next post we would see the life of each Ahl-ul-bayt right from  Prophet Muhammad (s.a.w.s) to the Imam of present age Imam Mohammad al-Mahdi(a.s)