Hawzah News Agency – The commander of the faithful, Imam Ali peace be upon him says:

إنّ الإيمانَ يَبْدو لُمْظَةً بَيْضَاءَ في القلبِ، فكلَّما ازْدادَ الإيمانُ عِظَماً ازْدادَ البَياضُ، فإذا اسْتُكْمِلَ الإيمانُ ابْيَضَّ القلبُ كُلُّهُ.

'Faith appears as a white spot in the heart. So whenever faith increases in magnitude, the whiteness increases. When faith is completed, the entire heart becomes white.'

Source: Kanz al-Ummal, no. 1734