Quran states ahlul bayt are free from rijs, therefore infallible.
Who are ahlul bayt?
They are Muhammad, Ali, Fatima, Hasan and Husain.
can you elaborate more on infallibility ?
infallible in worldly matters or spiritual matters or both ?
My conclusion is based on the ayat of Tatheer (33:33) and the hadith of Ahlul Kisaa taken together. The ayat identifies ahlul bayt as being 'purified' and the hadith identifies Panjatan as ahlul bayt.
How does purity imply infallibility? I would like to post an extract which I had posted on the Shiachat forum during a debate with anajmi there:
Now, to the last two sentences of the ayat 33:33.
إِنَّمَا يُرِيدُ اللَّهُ لِيُذْهِبَ عَنْكُمُ الرِّجْسَ أَهْلَ الْبَيْتِ وَيُطَهِّرَكُمْ تَطْهِيرًا
1. Indeed, Allah wants banishment of ‘rijs’ from you, O ahl-al-bayt.
2. And, (Allah wants) you purified to perfection.
Allah indeed says “He wants”. Now, if Allah desires anything, it automatically comes to pass unless it refers to the behavior of human beings still alive. That is because, humans can thwart Allah’s will. However, in this ayat, he addresses those people, including the Prophet, whom He knows will always act in accordance with His will.
First sentence: Indeed, Allah wants banishment of ‘rijs’ from you, O ahl-al-bayt.
What did Allah remove from them? It was ‘rijs’. Translators use dictionary meanings like filth and abomination. In fact this cannot be the meaning here. “Rijs” refers to “unbelief in Allah and His message”. Hence, Allah is saying that ahl-ul-bayt can be relied upon to be the perfect guide from now on. In the hadith of ahl-ul-kisaa, Nabi says that Ali, Fatima, Hasan and Husain are his ahl-al-bayt. He actually does not include himself although that is clearly implied.
Support for rijs=unbelief comes from ayat 6:125
يَجْعَلُ اللَّهُ الرِّجْسَ عَلَى الَّذِينَ لا يُؤْمِنُونَ
Allah places “rijs” on unbelievers. Hence unbelief and “rijs” go together.
Second sentence: And, (Allah wants) you purified to perfection.
So, not only has any trace of “unbelief’ been removed from ahl-ul-bayt, but also they have been purified to utmost perfection. Allah thus blesses his perfect believers with the quality of never committing an error that might tempt even His strongest believers.
In conclusion, Allah’s wish is His command and it always comes to pass. And he has rendered Panjatan perfect among believers and perfect in adhering to the behavior that Allah demands from His devotees.
Infallibility is in both spiritual and worldly matters as far as Panjatan are concerned. No matter what the issue, spiritual or worldly, they always acted in accordance with Allah's will.
Infallible = free from rijs = free from any trace of unbelief = acting always in the manner worthy of Allah's confidence in them.
An Arabic word related to 'infallible' is 'ma'soom'. This means 'protection from sin'. It has the same connotation as 'infallible' and is used as a synonym for 'free from rijs'.