Al-Kāfi - Volume 1 > Chapter on the quality of knowledge its virtue and the virtue of the scholars
Hadith #6

6ـ أَحْمَدُ بْنُ إِدْرِيسَ عَنْ مُحَمَّدِ بْنِ حَسَّانَ عَنْ إِدْرِيسَ بْنِ الْحَسَنِ عَنْ أَبِي إِسْحَاقَ الْكِنْدِيِّ عَنْ بَشِيرٍ الدَّهَّانِ قَالَ قَالَ أَبُو عَبْدِ الله (عَلَيْهِ السَّلام) لا خَيْرَ فِيمَنْ لا يَتَفَقَّهُ مِنْ أَصْحَابِنَا يَا بَشِيرُ إِنَّ الرَّجُلَ مِنْهُمْ إِذَا لَمْ يَسْتَغْنِ بِفِقْهِهِ احْتَاجَ إِلَيْهِمْ فَإِذَا احْتَاجَ إِلَيْهِمْ أَدْخَلُوهُ فِي بَابِ ضَلالَتِهِمْ وَهُوَ لا يَعْلَمُ.

6. Ahmad ibn Idris has narrated from Muhammad ibn Hassa’n from Idris ibn al-Hassan from abu Ishaq al-Kindi from Bashir al-Dahhan from abu ‘Abdallah (a.s.) who has said the following. “O Bashir, there is nothing good in those of our people who do not acquire (Fiqh) good understand of religion. If one of them would not have good understanding of the religion he would need to ask those who oppose us. When he would need them they would lead him into their straying ways in a manner that he would not even realize.”