Al-Kāfi - Volume 1 > Chapter on the Qualities of the Scholars
Hadith #5

5ـ أَحْمَدُ بْنُ عَبْدِ الله عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ الْبَرْقِيِّ عَنْ بَعْضِ أَصْحَابِهِ رَفَعَهُ قَالَ قَالَ أَمِيرُ الْمُؤْمِنِينَ (عَلَيْهِ السَّلام) لا يَكُونُ السَّفَهُ وَالْغِرَّةُ فِي قَلْبِ الْعَالِمِ.

5. Ahmad ibn ‘Abdallah from Ahmad ibn Muhammad al-Barqi from certain persons of his people in a marfu‘ manner (rafa’ahu) from Amir al-Mu’minin Ali (a.s.) who has said the following. “Foolishness and arrogance are not found in the hearts of the scholars.”