Certainly the deeds of the people have affects the worldly life as well as the Hereafter, and they assume a shape of a body etc. So that he may be thrown into the Hell-fire forever; the fire whose fuel are men and stones. Or he may enter the Paradise of ‘Adn Naeem’. All these effects could be seen only by the righteous servants of Allah. These spur them to good deeds and protect themselves from sin and iniquity. This vision has been bestowed upon those servants of Allah who had seen this proof. They have preferred the wish of Allah upon their selfish desires.
This is the reason that the pious servants of Allah cannot commit a sin. Their example is that of a person with a normal vision in company of a blind man. Both are walking together on a path having numerous potholes any pits. The person having sight sees these perils; he saves himself and advises his companion to save himself too.
It can also be compared to some thirsty people who have before them water and they wish to drink it to quench their thirst. One of these people is a doctor who has an instrument, which can detect the various dangerous germs in the water, and he warns his friends to avoid this water and tells them to clean the water before drinking it. In the same way is the example of the righteous servants who have seen the Proof of Allah and the good and bad effects of a deed.
With this vision they are able to perceive the actual evil behind the sinful acts as if they see it with their own eyes; they can see the evil personified and being thrown in the fire of Hell. Therefore how is it possible for them to do such a thing intentionally or commit an act, which has been prohibited by Allah.
Whatever doubts are being presented regarding the infallibility of the Prophets are based on ambiguous ayats. They have erred in their interpretation, sometimes they have erred in tafsir by following the concocted traditions or reports. Since we do not wish to prolong the discussion we shall present only two such examples.