Amīr al-mu’minīn's wisdom on knowledge and virtue
Nahj al-Balāgha|Volume 1|Book 3|Chapter 147
يَا كُمَيْل بْن زِيَادٍ، إِنَّ هذهِ الْقُلُوبَ أَوْعِيَةٌ فَخَيْرُهَا أَوْعَاهَا فَاحْفَظْ عَنِّي مَا أَقُولُ لَكَ:
O Kumayl, these hearts are containers. The best of them is that which preserves (its contents). So, preserve what I say to you: