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Shiavault - a Vault of Shia Islamic Books Hayat Al-Qulub Vol.3 Part 2: The Imam should be Infallible (inerrant-sinless) from all sins We should know that the Imamite scholars have all agreed that an Imam is always immaculate from all small or big sins right from his childhood to the end of his life. He commits no sin either wilfully or by mistake. None except Ibne Babawayh and his teacher Muhammad bin Al Hasan (r.a.) have differed from this opinion.
These gentlemen have justified that excepting the Divine Commandments and the propagation of Divine Messages, it is permissible that due to some hidden wisdom they (Imams) can commit a sahv (slight oversight). For example Sahv is allowed in Prayer and all other worship acts. But white explaining or describing of the orders (divine) and in the propagation of the divine message, they do not admit any kind of mistake on the part of Imam.
Excepting the Ismailis all Islamic sects do not consider infallibility as a condition of Imamate. According to the Imamis there are many logical as well as Naqali (narrative) arguments in support of this belief. Some of them have been described in volume one. Yet we quote some arguments below: First Argument The Imam is appointed because the people can make a mistake. So there must be someone to protect them.
But if that person were also likely to make mistake then he too will be in need of another Imam, leader or guide. Therefore it will require either continuity of such appointments which is impossible or, ultimately, such an Imam will have to be there who cannot err and then only will he be the Imam. Second Argument The Imam is the guardian or protector of the Shariat because the Holy Quran does not contain details of the Shariat rules.
Similarly each and every detail of Divine code of conduct cannot be drawn from the Sunnah and traditions of the Holy Prophet (S) nor can they be known through the Ijma (consensus) of the Ummah. It is so because, in a gathering wherein there is no Imam, and when everyone can err the entire gathering of such fallible persons can also err. The required details cannot be known from Qiyas (analogy) because, in arguments, in principles, deeds done according it have been proved wrong.
Even if it is taken for granted it is impossible to guard and guide all the orders of the Shariat nor of the original clearance (Baraat-e-Asaliyah) because had it been possible to be acted upon it, the appointment of prophet would not have been necessary.