How can one respond to someone who claims that the outward does not affect the inward, guided by the words of Ibn Taymiyyah, what is mentioned in the Book and the Sunnah, and the sayings of the people of knowledge?

The work and rectification of the heart are among the most important matters. The possessor of a sound heart is one who is obedient and performs righteous deeds, because the outward is a reflection of the inward, and the corruption of the outward is an indication of the corruption of the inward. However, a servant might perform outward deeds while his inward is corrupt, like the hypocrites. The importance of the heart is indicated by the Prophet's (peace be upon him) saying: "You shall straighten your rows, or Allah will cause disagreement between your hearts," and his saying: "Indeed, Allah does not look at your forms or your wealth, but He looks at your hearts and your deeds."