Just as the body has physical diseases, the heart has spiritual diseases. Fiqh-ul-Quloob identifies diseases like:

(jurisprudence) which deals with external actions like prayer and trade, Fiqh al-Qulūb

For those seeking structured study material in English, the following resources provide translations and explanations:

(The Jurisprudence of Hearts) is an Islamic spiritual science focused on the "actions" of the heart, such as sincerity, love for God, and patience. Unlike traditional jurisprudence ( Fiqh ) which governs physical acts, this discipline seeks to rectify the internal state to ensure external worship is meaningful. English PDF Resources

For those searching for the PDF, it is important to look for verified translations that preserve the integrity of the Sheikh’s original insights. Many Islamic digital libraries and educational platforms host these files to facilitate dawah and spiritual growth. By studying Fiqh-ul-Quloob, a reader does not just learn about Islam; they learn how to feel Islam. It is an essential resource for anyone looking to purify their heart from the diseases of pride, envy, and attachment to the worldly life, replacing them with a tranquil heart that finds rest only in the remembrance of Allah.

A central tenet of this knowledge is that the corruption of the limbs stems from the corruption of the heart. If the heart is sound, the actions of the body will be sound. This is based on the famous Hadith of the Prophet Muhammad (peace be upon him):