Hawzah News Agency – The merciful prophet of Islam, peace be upon him and his household says:

جَلاءُ هذهِ القُلوبِ ذِكرُ اللَّهِ وتِلاوَةُ القرآنِ.

'The polish of these hearts is the remembrance of Allah and the recitation of the Quran.'

Source: Tanbih al-Khawatir, v. 2, p. 122