Sayyiduna Abu Hurayrah (may Allah be pleased with him) and Sayyiduna Abu Dharr al-Ghifari (may Allah be pleased with him) say: "A single chapter of knowledge that a man learns is dearer to me than (offering) a thousand voluntary rak'ahs."
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب العلم / 507