Infallibility is the abstinence from sins and disobedience of Allah (s). Belief in the Infallibility of the Prophets (s) and the Masumin (a) is part of the Shia creed. They believe that Prophets (s) and Imams (a) are Divine leaders who have the ability to commit sins, but are protected by Allah from it. With this grace bestowed upon them due to their worthiness, they do not even consider committing a sin. It is a state that is higher than taqwa or piety. It prevents the person from doing anything wrong, even a wrong thought. The necessity of infallibility is obvious. For a leader to be trusted and followed, the leader must be sinless. Otherwise, it would cause doubt in the messenger and in the message itself. The Imams (a) are Divine guides with the duty to help people stay on the path taught by the Prophet (s). Necessity of the Infallibility of the Imams (a) follows that of the Prophet (s).
The following are some arguments for the infallibility of the Imams (a):
Arguments from authoritative texts
1) Prophet Ibrahim’s (s) request for Imams (a) from his progeny and Allah’s answer. And when his Lord tested Ibrahim with certain words, and he fulfilled them, He said, ‘I am making you the Imam of mankind.’ Said he (Ibrahim), ‘And from among my descendants?’ He said, ‘My pledge does not extend to the unjust. (2:124)
2) Whoever commits a sin has committed injustice – and whoever transgresses the bounds of Allah, it is they who are the unjust. (2:229). One who commits injustice cannot be an Imam (a), as explained by the Quran – My pledge does not extend to the unjust. (2:124)
3) The verse of Ulil Amr – O you who believe! Obey Allah and obey the Apostle and those vested with authority among you. (4:59). This verse links obedience to the Prophet (s) with obedience to a certain group of people who have been given authority with no conditions. This would not be applicable if the people vested with authority (Imams (a)) were not sinless.
4) Hadith of the Prophet (s) – I have left among you two things, you will never go astray after me, should you hold onto them. These are two weighty things, the one which is greater than the other, is the Book of Allah, an extended rope from heaven to earth and my ‘Itra, Ahl al-Bayt (household), be aware that they will not separate till the time they meet me near the al-Hawdh (pond).
(This hadith has been narrated in Mustadrak al-Hakim, vol. 3, p. 148; As-Sawa‘iq al-Muhriqah, Book 11, Chapter 1, p. 149. There is also a similar text in Kanz al-‘Ummal, vol. 1, Bab “Al-I‘tisam bi’l-Kitab wa’s-Sunnah”, p. 44; Musnad Ahmad ibn Hanbal, vol. 5, pp. 182, 189; and others)
1) A leader has to be of the highest standards in that which he wants to lead. For people to trust and follow the leader, it would require that they be sinless.
2) If an Imam makes a mistake or commits sins, he would need another person to guide him. Such a person cannot be an Imam (a) sent by Allah to guide people.
3) If an Imam (a) commits a sin the people have two choices; either they follow him in that sin or they turn away from him in that matter. Both of these choices would be wrong for them as followers of a Divinely sent Imam (a).