How can one achieve soundness of heart?

Purity of heart means it is free from ill-will, malice, envy, and hatred towards Muslims. It brings comfort to the heart and pleasantness to the soul. The fundamental principle for a Muslim is to have a pure heart towards his brethren, forgiving them. It is one of the qualities of the people of Paradise, as Anas ibn Malik narrated about the man whom the Prophet (peace be upon him) testified would enter Paradise. The reason for this was that the man found no deceit in his heart towards any Muslim, nor did he envy anyone for any good Allah had bestowed upon them.

Ibn Juzayy al-Maliki considered purity of heart among the Sharia commands related to the hearts, as it yields a pleasant soul, a cheerful countenance, and the desire for good for everyone, and it removes animosity, hatred, and envy.