The intellect is located in the heart Al-Adab Al-Mufrad 547
Arabic hadith text
حَدَّثَنَا سَعِيدُ بْنُ أَبِي مَرْيَمَ، قَالَ: أَخْبَرَنَا مُحَمَّدُ بْنُ مُسْلِمٍ قَالَ: أَخْبَرَنِي عَمْرُو بْنُ دِينَارٍ، عَنِ ابْنِ شِهَابٍ، عَنْ عِيَاضِ بْنِ خَلِيفَةَ، عَنْ عَلِيٍّ رَضِيَ اللَّهُ عَنْهُ، أَنَّهُ سَمِعَهُ بِصِفِّينَ يَقُولُ: إِنَّ الْعَقْلَ فِي الْقَلْبِ، وَالرَّحْمَةَ فِي الْكَبِدِ، وَالرَّأْفَةَ فِي الطِّحَالِ، وَالنَّفَسَ فِي الرِّئَةِ.
Translation
'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."