The history of mankind is full of names that gained the admiration and veneration of their people because they saw in them the example and model they seek. On top of such personalities come the Prophets and Messengers of Allah who reached the highest level of human conduct and character. As recipients and conveyers of the divine revelation, they were infallible; moreover, they were raised to be followed and imitated.
However, other people, no matter how holy, pious and venerated they may be in the eyes of their people, cannot be infallible. Unfortunately, some Muslim sects and groups have exaggerated their admiration of certain pious people and raised them to the status of Prophets and Messengers. Even some went to the extreme and gave them an even higher rank, which reveals confusing and unbalanced belief.
On this issue, Dr. Hatem Al-Haj, professor of Fiqh said:
There is no indication in the Qur’an or authentic Sunnah that anyone is infallible except the Messengers and Prophets. They are completely infallible regarding the transmission of the revelation. It is also impossible for them to fall into the enormities the People of the Book attributed to them. That is because they were meant to be role models for the people and Almighty Allah would not send defective role models who commit disgraceful sins like incest.
The imams of the Shiite are great righteous descendants of the Prophet (peace and blessings be upon him), and they never claimed that they were infallible, nor will you be able to find any proof in the revelation to support that claim.