

Allah only desires to keep away the uncleanness from you, O people of the House! and to purify you a (thorough) purifying. [Holy Quran 33:33]
Conversation between Imam Ali(as) and Abu Bakr(la)
Imam Ali(as): Have you read the book of Allah(swt)?
Abu Bakr(la): Yes.
Imam Ali(as): The Ayat of Tatheer (i.e. 33:33) has been send down in our praise or in the praise of others?
Abu Bakr(la): Yes, in Your praise.
Imam Ali(as): If a witness, witnesses against Janabe Fatima(sa) regarding a bad thing, what will you do in that case?
Abu Bakr(la): I will apply the Islamic Had on her(sa) just like its done for other muslim women.
Imam Ali(as): In that case you will be among the Kaafir in the sight of Allah(swt).
Abu Bakr(la): No.
Imam Ali(as): Because in this case you rejected the declaration of Allah(swt) regarding the Purity of Janabe Fatima(sa) , accepting the declaration of the common people.
[ Ref: Ihtijaaj-e-Tabarisi Vol 1 , Pg: 120 ]
So it can be concluded that when we come across any incident which states that a
wrong deed ( Gunah ) has been committed by any of the MASOOMS (those included in Aayate Tatheer), and if we accept it , then as per the above Proof given by Imam Ali(as) we will become a KAFIR!!!!!!!!!!!