Shaykh al-Islam Abū al-ʿAbbās Aḥmad ibn Taymiyyah al-Ḥarrānī al-Dimashqī said:

Praise belongs to Allah, Lord of all worlds, and may Allah’s blessings and peace be upon our master Muḥammad and his family.

Section: Concerning the Almighty’s words,
“ We never sent before you any messenger or prophet without Satan throwing something into his recitation when he was reciting … ”
up to His saying,
“ … so that He may make what Satan casts a trial for those whose hearts are diseased and whose hearts are hard; and the wrongdoers are indeed in far-reaching dissension, ”
and His saying,
“ and so that those who have been granted knowledge may know that it is the truth from your Lord, and therefore believe in it, and their hearts humble themselves to it; for Allah surely guides those who believe to a straight path.”

Allah has divided hearts into three categories: hardened hearts, hearts afflicted with disease, and believing hearts that are humble. A heart is either dry and rigid, refusing to soften before the truth in acknowledgment and submission, or it is not dry and rigid.

The first type is the hardened heart—stiff and dry like stone. Faith cannot imprint itself upon it, nor can knowledge be inscribed in it, because such inscription requires a soft and receptive vessel.