'Iyad ibn Khalifa heard 'Ali say at Siffin, "The intellect is located in the heart. Mercy is located in the liver, Compassion is located in the spleen. The self (nafs) is located in the lungs."  

أَنَّهُ سَمِعَهُ بِصِفِّينَ يَقُولُ إِنَّ الْعَقْلَ فِي الْقَلْبِ وَالرَّحْمَةَ فِي الْكَبِدِ وَالرَّأْفَةَ فِي الطِّحَالِ وَالنَّفَسَ فِي الرِّئَةِ