For a person cannot establish that he knows by means of a proof: his knowledge of that proof’s premises requires him to find within himself that he knows them. If knowing that he knows required a proof, this would lead to circular reasoning or an infinite regress. For this reason, a person does not perceive the presence of knowledge when its cause is present, if that knowledge is self-evident, or when he knows the two premises, if it is inferential. This argument has been used against those who deny that reasoning yields knowledge, although this question requires distinctions that are beyond the scope of the present discussion.
The point is that whoever considers a proof that yields knowledge finds within himself that he knows upon understanding that proof, just as he finds himself hearing and seeing when listening to a sound or looking for the sun, the crescent moon, or something else. Knowledge arises in the soul, as do all other perceptions and movements, through the causes Allah appoints. Most of this occurs through the angels of Allah Most High. Through them, Allah, glorified is He, sends down upon His servants’ hearts whatever knowledge, strength, and other things He wills. Hence the Prophet, may Allah bless him and grant him peace, said concerning Hassān:
“O Allah, strengthen him with the Holy Spirit.”
Allah Most High says:
“He has inscribed faith in their hearts and strengthened them with a spirit from Him.”
And the Prophet, may Allah bless him and grant him peace, said:
“Whoever seeks judicial office and seeks assistance in obtaining it is left to bear it unaided. But whoever neither seeks judicial office nor seeks assistance in obtaining it, Allah sends down an angel to guide him aright.”
ʿAbd Allāh ibn Masʿūd said:
“We used to say that tranquillity speaks through ʿUmar’s tongue.”
Ibn Masʿūd also said:
“The angel has a prompting, and Satan has a prompting. The angel’s prompting is a promise of good and an affirmation of the truth. Satan’s prompting is a promise of evil and a denial of the truth.”
This statement made by Ibn Masʿūd is reliably transmitted