Hawzah News Agency - Ahmad ibn ’Idris has narrated from Muhammad ibn ‘Abd al-Jabbar, from one of our people in a marfu’ manner that Abu 'Abdillah (al-Sadiq) 
was asked, 'What is intellect (al-'Aql)?'. He said:
مَا عُبِدَ بِهِ الرَّحْمَنُ وَاكْتُسِبَ بِهِ الْجِنَانُ قَالَ قُلْتُ فَالَّذِي كَانَ فِي مُعَاوِيَةَ فَقَالَ تِلْكَ النَّكْرَاءُ تِلْكَ الشَّيْطَنَةُ وَهِيَ شَبِيهَةٌ بِالْعَقْلِ وَلَيْسَتْ بِالْعَقْلِ.
‘It is what someone worships ar-Rahman with and attains paradise.’ I then asked, 'What was the thing within Mu'awiya?'. He replied, ‘That was heinousness, that was devilry and it is similar to the intellect but it is not intellect.’
Al-Kāfi, v.1