“Knowledge is of two kinds: that which is absorbed and that which is heard. And that which is heard does not profit if it is not absorbed.”

The saying is transmitted in the adab and knowledge literature attributed to ‘Ali ibn Abi Talib (may Allah be pleased with him), the Prophet’s cousin and the fourth caliph. The Arabic distinguishes ‘ilm matbu‘ from ‘ilm masmu‘ — knowledge stamped into a person against knowledge that merely reached his ears. Collections of his sayings preserve it, though a single early source for the wording is not pinned down.