Allah (The Most High) says, قَدۡ أَفۡلَحَ مَن زَكَّٮٰهَا (٩) وَقَدۡ خَابَ مَن دَسَّٮٰهَا (١٠)
He has succeeded who purifies it [The heart], and he has failed who instills it [with corruption]. {Quran 91: 9–10}
The Prophet Muhammad (s) said, أَلاَ وَإِنَّ فِي الْجَسَدِ مُضْغَةً إِذَا صَلَحَتْ صَلَحَ الْجَسَدُ كُلُّهُ وَإِذَا فَسَدَتْ فَسَدَ الْجَسَدُ كُلُّهُ أَلاَ وَهِيَ الْقَلْبُ
“Beware! In the body, there is a piece of flesh which, if it is sound, the whole body will be sound, and if it is corrupt, the whole body will be corrupt. It is the heart.”
{Bukhari & Muslim}
