Al-Nu’man ibn Bashir reported: The Messenger of Allah, peace and blessings be upon him, said:
أَلَا وَإِنَّ فِي الْجَسَدِ مُضْغَةً إِذَا صَلَحَتْ صَلَحَ الْجَسَدُ كُلُّهُ وَإِذَا فَسَدَتْ فَسَدَ الْجَسَدُ كُلُّهُ أَلَا وَهِيَ الْقَلْبُ
Verily, in the body is a piece of flesh which, if sound, the entire body is sound, and if corrupt, the entire body is corrupt. Truly, it is the heart.
Source: Ṣaḥīḥ al-Bukhārī 52, Grade: Muttafaqun Alayhi
