The Islamic belief is that Prophets were infallible. This is used with the meaning that while they enjoyed free will and desire, they never committed sins. Since prophets are the messengers of God and practical role models for people, it would be illogical for them to be sinful. For if the messengers themselves were sinful, we would have no point of reference for which actions are good and which are evil. Furthermore, if there was a possibility that they may lie, this would jeopardise the Divine message in its totality.
Prophets were the guides for mankind and hence they ought to enjoy the highest degree of knowledge which is free from all types of insufficiency and error. The knowledge of the Prophets covers all that mankind needs for the prosperity of their life, both in this world and the hereafter. All the Prophets were unlettered; i.e. they did not gain their knowledge in an ordinary academic fashion.
To this end, Allah, the Almighty has equipped them with a Divine knowledge which is obtained through revelation, intuition and extraordinary knowledge.
The third distinguishing characteristic of the Prophets is a miracle. Miracle in Arabic is ‘Mo’jeza’ which literally means an act that others are incapable of doing and hence they relinquish upon witnessing it. The Holy Quran uses the term ‘Ayah’ (Sign) to express a miracle, as miracles are the signs of God to prove the true claim of His Messengers. All miracles performed by the Prophets only occurred by the Leave of God. Although miracles violate the normal natural laws and hence may be scientifically impossible, they are not logically impossible. Miracles also do not violate the law of causality. The occurrence of miracles has its own reasons, though these reasons are metaphysical.