If a person has some hardness in his heart, what affairs would soften it?
Nothing better and more essential than the Noble Qur’aan for it is what softens the hearts.
Allaah—جل وعلا—has said:
(الَّذِينَ آمَنُوا وَتَطْمَئِنُّ قُلُوبُهُمْ بِذِكْرِ اللَّهِ أَلا بِذِكْرِ اللَّهِ تَطْمَئِنُّ الْقُلُوبُ)،
“Those who believe (in the Oneness of Allah – Islamic Monotheism), and whose hearts find rest in the remembrance of Allah, Verily, in the remembrance of Allah do hearts find rest.” —Ra’ad: 28
So, that which softens the hearts is the Qur’aan, which if Allaah was to send down
(عَلَى جَبَلٍ لَرَأَيْتَهُ خَاشِعاً مُتَصَدِّعاً مِنْ خَشْيَةِ اللَّهِ)،
“…on a mountain, you would surely have seen it humbling itself and rending asunder by the fear of Allah.” —Al-Hashr: 21
Likewise [from what softens the hearts is] sitting with the righteous, attentively listening to the Qur’aan, admonitions and reminders. And these are from the affairs that soften the hearts.
Source: From the official website of Ash-Shaykh Saalih ibn Fawzaan Al-Fawzaan—حفظه الله.