It is narrated from the holy Prophet of Islam (PBUH) who said:

The best of the hearts is the heart that has more capacity for good, and the worst of the hearts, is the heart that has more capacity for bad. Therefore, the best of the hearts is the heart that has good in itself and is full of goodness. If speaks, it deserves reward, and if is silent, its silence is also deserves reward [1].

[1] Jaafariyat, Page 168.

Source:en.shafaqna.com