Assalaamu alaykum. I have been blessed with much guidance from Allah, The Exalted, Maa Shaa Allah. I have a question regarding the brain, the main tool for our rationality, with the mercy of Allah, The Exalted. I would like to know how to purify the brain; for example, for purifying the body, we perform Ghusl (ritual bath); for the heart, we ask for forgiveness; for our soul, we have the Quran, but I want to purify the main tool for our rationality, with which we do all work. I have a lot of matter which is unrelated or guides me to falsehood. I know most verses and most supplications, but I want a deeper medicine. Please, I require an answer from deeper within Islam. I am unable to explain my problem; please understand.

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.

We believe, dear brother, that by 'brain' you mean the mind. You should know – may Allah guide us and you to all that is good – that the real place of the mind is in the heart. This is the preponderant view of scholars, and it was indicated in the verse (that means): {So have they not traveled through the earth and have hearts by which to reason and ears by which to hear? For indeed, it is not eyes that are blinded, but blinded are the hearts which are within the breasts.} [Quran 22:46] There are many other pieces of evidence that the scholars mentioned in this regard. It should be noted that although the mind lies in the heart, it is connected to the brain.

Among the things that benefit your mind the most are the following:

First, acquiring knowledge and wisdom from their source, which is the divine revelation as expressed in the Quran and the Sunnah.

Al-Qaasimi said, "Fat-h Al-Mawsili said, 'Does not a sick person who is deprived of food and drink die? It is the same with the heart: if it is kept from wisdom and knowledge for three days, it dies.' He has indeed spoken the truth; knowledge and wisdom are the nourishment of the heart, and they sustain its life, just as food is the nourishment of the body. If a person has no knowledge, his heart is sick and its death is certain..." [Mawʻithat Al-Mu'mineen min Ihyaaa' ʻUloom Ad-Deen]

Second, the greatest knowledge of all is knowledge of Allah, the Exalted, which generates mindfulness and fear of Allah as well as knowledge of His rulings.

Ibn Rajab said:

"Imaam Ahmad used to say about Maʻroof, 'He has been endowed with the essence of knowledge, namely, the fear of Allah. The essence of knowledge is the knowledge about Allah that necessitates fearing Him, loving Him, drawing close to Him, finding comfort in Him, and yearning for Him. Next to it is knowledge of His rulings and what pleases Him of words, deeds, states, and beliefs. Whoever has realized these two branches of knowledge (knowledge of Allah and knowledge of His rulings), his knowledge is beneficial knowledge. He attains beneficial knowledge and a solemn heart." [Fadhl ʻIlm As-Salaf ʻala ʻIlm Al-Khalaf]

Third, carrying out good deeds; Allah, the Exalted, says (what means): {Whoever does righteousness, whether male or female, while he is a believer - We will surely cause him to live a good life...} [Quran 16:97]

As-Saʻdi commented on the verse saying, "The believer is blessed with a good life through serenity of the heart, comfort of the soul, and disregard for what distracts and confuses his heart..." Ibn ʻAbbaas, may Allah be pleased with him, said, "Verily, a good deed brightens the face and illuminates the heart..."

Fourth, the remembrance of Allah (Thikr), the best means of which is reciting the Quran.

Ibn Al-Qayyim said, "The hearts and graves are not illuminated with a better source of light than the remembrance of Allah. Allah, the Exalted, says (what means): {And is one who was dead and We gave him life and made for him light by which to walk among the people like one who is in darkness, never to emerge therefrom?} [Quran 6:122]" [Al-Waabil As-Sayyib]

Fifth, avoiding sins and misdeeds and shunning excessive sleep and excessive talk and the like of idle activities that are of no real benefit and may, rather, cause harm. Allah, the Exalted, says (what means): {No! Rather, the stain has covered their hearts of that which they were earning.} [Quran 83:14]

Ibn Al-Qayyim said about the effects of sins, "One of them is a sense of estrangement that the sinner finds in his heart between him and his Lord that cannot be compensated by any worldly pleasure..."

These are some religious means to nourish the mind. There are worldly means as well, including: maintaining a healthy diet and protecting the body from ailments and evils. It is said that a sound mind is in a sound body. Another beneficial means is enhancing the mind through mental exercises.

Allah knows best.