Some people criticize the Shia for believing that the Imams of the honorable Prophet’s family were infallible.
The Shia believe that the Imam, who has been appointed by Allah, must be infallible. Allah says:
Surely, I will make you an Imam of men. Ibrahim said, “and of my offspring?’ My covenant does not include the unjust, said He. (Qur’an 2:124)
And whoever goes beyond the limits of Allah, he indeed does injustice to his own soul. (Qur’an 65:1)
And whoever exceeds the limits of Allah those are they that are the unjust. (Qur’an 2:229)
Infallibility was a condition for the divine Imamate and it was limited, after Prophet Muhammad (s), to the Twelve Imams for no one else was infallible other than them according to consensus. In addition to this, the Qur’anic verse; Allah only desires to keep away uncleanness from you, O People of the House, and to purify you with a thorough purification. 33:33, confirms that Imam Ali, Imam Hasan and Imam Husayn were infallible. Many prophetic traditions also confirm the infallibility of the Twelve Imams (peace be upon them).
The previously mentioned verse provides proof of the infallibility of the Prophet’s family. It also shows that their purification is from Allah and is not a legislative matter, because the legislative will of purification from uncleanness does not concern the Prophet’s family alone, but includes all people. The legislative will also concerns one’s own actions whereas this Qur’anic verse shows that Allah’s will in purifying these persons from any uncleanness is His creative will. Allah says,
His command, when He intends anything, is only to say to it, “Be,’ and so it is. (Qur’an 36:82)
Of course, what is intended by uncleanness is not bodily uncleanness, but the internal uncleanness which is blasphemy, disbelief, guilt, disobedience, and everything sinful.
If one says that the purification might mean that Allah would forgive their sins.
I would answer that forgiveness does not purify uncleanness from the soul of the disobedient, but it takes the punishment away from him. Besides, forgiving a sin would not exist unless the sin had been committed. So, the sinful is not purified during committing the sin, while the Qur’anic verse indicates a complete purification.