Al-Kāfi - Volume 1 > Chapter on Utilization of Knowledge
Hadith #7

7ـ عِدَّةٌ مِنْ أَصْحَابِنَا عَنْ أَحْمَدَ بْنِ مُحَمَّدِ بْنِ خَالِدٍ عَنْ أَبِيهِ عَمَّنْ ذَكَرَهُ عَنْ مُحَمَّدِ بْنِ عَبْدِ الرَّحْمَنِ بْنِ أَبِي لَيْلَى عَنْ أَبِيهِ قَالَ سَمِعْتُ أَبَا جَعْفَرٍ (عَلَيْهِ السَّلام) يَقُولُ إِذَا سَمِعْتُمُ الْعِلْمَ فَاسْتَعْمِلُوهُ وَلْتَتَّسِعْ قُلُوبُكُمْ فَإِنَّ الْعِلْمَ إِذَا كَثُرَ فِي قَلْبِ رَجُلٍ لا يَحْتَمِلُهُ قَدَرَ الشَّيْطَانُ عَلَيْهِ فَإِذَا خَاصَمَكُمُ الشَّيْطَانُ فَأَقْبِلُوا عَلَيْهِ بِمَا تَعْرِفُونَ فَإِنَّ كَيْدَ الشَّيْطَانِ كَانَ ضَعِيفاً فَقُلْتُ وَمَا الَّذِي نَعْرِفُهُ قَالَ خَاصِمُوهُ بِمَا ظَهَرَ لَكُمْ مِنْ قُدْرَةِ الله عَزَّ وَجَلَّ.

7. A number of our people has narrated from Ahmad ibn Muhammad ibn Khalid from his father from the one mentioned from Muhammad ibn ’Abd al-Rahman ibn abu Layla from his father who has said the following. “Imam abu Ja‘far (a.s.) has said, ‘When you hear knowledge you must utilize it and your hearts must become more open. When knowledge increases in one’s heart it becomes harder to bear and Satan may over power him. If Satan would dispute with you move on him with whatever you know. The plots of Satan are weak.” I asked the Imam (a.s.) “What is it that we know?’” The Imam replied, “Fight him with whatever of the power of Allah, the Majestic, the Glorious, has come to light before you.”