Know that man’s essence, in his original condition, is created in blank simplicity without any information about the world’s of God. Man gets his information about the world’s by means of perception. Man is created with the sense of touch, of sight, of sense, of hearing, of taste, and of intellect.
Beyond the state of intellect there is another stage. In this stage another eye is opened, by which man sees the hidden, and what will take place in the future, and other things, from which the intellect is as far removed as the power of discernment is from the perception of intelligibles and the power of sensation is from things perceived by discernment.
The very essence of ignorance is for a man to have no supporting reason except that it is a stage he himself has not attained and for him it does not exist; so he supposed that it does not exist in itself.
Now if a man born blind did not know about colors and shapes from constant report and hearsay, and were to be told about them abruptly, he would either understand them nor acknowledge their existence. But God has brought the matter within the purview of His creatures by giving them a sample of the special character of the prophetic power: sleeping. For the sleeper perceives the unknown that will take place, either plainly, or in the guise of an image the meaning if which is disclosed by interpretation.
If a man had no personal experience of dreaming and someone were to tell him: “There are some men who fall down unconscious as though they were dead, and their perception, hearing, and sight leave them, and they then perceive what is “hidden,” he would deny it and give apodeictic proof of its impossibility by saying: “The sensory powers are the causes of perception. Therefore one who does not perceive such things when his powers are present and functioning a fortiori will not perceive them when his powers are suspended.”
Just as the intellect is one of man’s stages in which he receives an “eye” by which he “sees” various species of intelligibles from which the senses are far removed, the prophetic power is an expression signifying a stage in which man receives an “eye” possessed of a light, and in its light the unknown and other phenomena not normally perceived by the intellect became visible.
– al Ghazali
In “Al Ghazali’s path to Sufism”