Al-Kāfi - Volume 1 > Chapter on the necessity to seek knowledge and the recommendations to learn
Hadith #3

3ـ عَلِيُّ بْنُ إِبْرَاهِيمَ عَنْ مُحَمَّدِ بْنِ عِيسَى عَنْ يُونُسَ بْنِ عَبْدِ الرَّحْمَنِ عَنْ بَعْضِ أَصْحَابِهِ قَالَ سُئِلَ أَبُو الْحَسَنِ (عَلَيْهِ السَّلام) هَلْ يَسَعُ النَّاسَ تَرْكُ الْمَسْأَلَةِ عَمَّا يَحْتَاجُونَ إِلَيْهِ فَقَالَ لا.

3. Ali ibn Ibrahim has narrated from Muhammad ibn ‘Isa from Yunus ibn ‘Abd al-Rahman from certain persons of his people who has said the following. “Abu al-Hassan (a.s.) was asked, “Is it permissible for people not to seek what (religious knowledge) they need?” The Imam (a.s.) said, “No, (it is not permissible to ignore learning).”