What is the best comprehensive book on the deeds of the heart (worship of the heart) to ensure that worship conforms to the Sharia without excess or deficiency?

The first book recommended for the topic of heart purification is the Holy Quran, for it is a healing for what is in the chests, and a guidance and mercy for the believers. It removes the diseases of desires and doubts and leads the heart to certainty. If the heart is purified, all the limbs are purified.

Furthermore, the guidance of the Messenger of Allah, peace and blessings be upon him, is a great educator.

Among the other books written on this topic are "Madarij al-Salikin" and "Al-Jawab al-Kafi," both by Ibn al-Qayyim, and all of his books are beneficial in this regard.

The purification of the heart is the greatest thing a servant strives to achieve, because with its purification, the rest of the body becomes purified, as the Messenger of Allah, peace and blessings be upon him, said: "Indeed, there is a piece of flesh in the body, if it is sound, the whole body is sound, and if it is corrupt, the whole body is corrupt. Indeed, it is the heart."