Al-Kāfi - Volume 1 > Chapter on the necessity to seek knowledge and the recommendations to learn
Hadith #5

5ـ عِدَّةٌ مِنْ أَصْحَابِنَا عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ الْبَرْقِيِّ عَنْ يَعْقُوبَ بْنِ يَزِيدَ عَنْ أَبِي عَبْدِ الله رَجُلٍ مِنْ أَصْحَابِنَا رَفَعَهُ قَالَ قَالَ أَبُو عَبْدِ الله (عَلَيْهِ السَّلام) قَالَ رَسُولُ الله (صَلَّى اللهُ عَلَيْهِ وَآلِه) طَلَبُ الْعِلْمِ فَرِيضَةٌ وَفِي حَدِيثٍ آخَرَ قَالَ قَالَ أَبُو عَبْدِ الله (عَلَيْهِ السَّلام) قَالَ رَسُولُ الله (صَلَّى اللهُ عَلَيْهِ وَآلِه) طَلَبُ الْعِلْمِ فَرِيضَةٌ عَلَى كُلِّ مُسْلِمٍ أَلا وَإِنَّ الله يُحِبُّ بُغَاةَ الْعِلْمِ.

5. A number of our people has narrated has narrated from Ahmad ibn Muhammad al-Barqi from Ya’qub ibn Yazid from abu ‘Abdallah, a man of our people narrated in a marfu‘ manner from abu ‘Abdallah (a.s.) from the Holy Prophet (s.a) who has said the following. “Seeking knowledge is obligatory.” In another Hadith Imam abu ‘Abdallah has narrated from the holy Prophet who said, “Seeking knowledge is obligatory for every Muslim. Let it be known that Allah loves those who seek knowledge.”