Reference: http://www.alfawzan.af.org.sa/node/14944
Question: If a person has harshness and cruelty in his heart [towards others], then what can soften his heart from this harshness and cruelty?
Response: There is nothing better nor befitting than the Noble Qur.aan; that is what shall soften his heart, as Allaah Jalla wa ‘Alaa said:
So that which softens the hearts is the Qur.aan, if Allaah were to reveal it;
And likewise the gatherings of the righteous, as well as listening to the Qur.aan, and listening to lectures [encouraging one another upon good], and the [general] remembrance [of Allaah] – this is what shall soften the hearts [in shaa.-Allaah].