Does a person think with their heart or with their mind, and what is the legitimate proof of that from the Qur'an and Sunnah?

The intellect is a spiritual light through which the soul perceives knowledge, and its seat is the heart. The Holy Quran and the Prophet's Sunnah have clarified that the heart is the center of understanding, thought, guidance, and misguidance. Among the verses that affirm this are the Almighty's saying: "They have hearts with which they do not understand," and His saying: "So that they may have hearts with which to reason." It is also mentioned in the prophetic tradition: "Indeed, there is a piece of flesh in the body which, if it is sound, the whole body is sound, and if it is corrupt, the whole body is corrupt. Indeed, it is the heart."

This view differs from the opinion of some philosophers and a few Muslims who claim that the intellect's seat is the brain. Although the intellect may be affected when the brain is affected, this does not mean that the brain is its seat. The soundness of the intellect is conditioned by the soundness of the brain, just as other organs are affected by brain dysfunction but are not a part of it.