Nahj al-Balāgha
Hadith 2200٣٣٨. وَقَالَ (عليه السلام): الْعِلْمُ عِلْمَانِ: مَطْبُوعٌ وَمَسْمُوعٌ وَلَا يَنْفَعُ الْمَسْمُوعُ إِذَا لَمْ يَكُنِ الْمَطْبُوعُ.
338. Amīr al-mu’minīn, peace be upon him, said: Knowledge is of two kinds — that which is absorbed and that which is just heard. The one that is heard does not give benefit unless it is absorbed.