How can a Muslim acquire a sound heart, and what can he do to achieve that, especially since his repeated supplications have not brought about a tangible change, but rather he continues to suffer from obsessive whispers that attack him severely after a period of calm?

A sound heart is one that will grant its possessor salvation on the Day of Judgment. Ibn al-Qayyim defined a sound heart as one that is free from every desire or doubt that contradicts Allah's command and prohibition, and whose servitude is purely for Allah alone, in will, love, and reliance, and that is free from submitting to anyone other than His Messenger.

A sound heart can be attained through: 1. Sincerity in actions for Allah alone. 2. Contentment with Allah's decree and destiny. 3. Recitation of the Holy Quran, which is a healing for the ailments of hearts and bodies. 4. Supplicating for a sound heart, as mentioned in the reported supplication, "And I ask You for a sound heart." 5. Remembering Allah the Almighty, for the likeness of one who remembers his Lord and one who does not remember Him is like that of the living and the dead.