Character
أَلَا وَإِنَّ فِي الْجَسَدِ مُضْغَةً إِذَا صَلَحَتْ صَلَحَ الْجَسَدُ كُلُّهُ، وَإِذَا فَسَدَتْ فَسَدَ الْجَسَدُ كُلُّهُ، أَلَا وَهِيَ الْقَلْبُ
Translation
Indeed, there is in the body a piece of flesh which, if sound, the whole body is sound, and if corrupt, the whole body is corrupt. Verily, it is the heart.
Narrator
An-Nu'man ibn Bashir
Source
Sahih Bukhari & Muslim
Bukhari 52, Muslim 1599