He said something like, that this is a good way to learn, because writing it down in the own words helps one to understand it.
I think it was Aristotle, but I dont know exactly any more.
History Stack Exchange is a question and answer site for historians and history buffs. It only takes a minute to sign up.Sign up to join this community
I wonder whether you mean John Locke's treatise on commonplace books?
As for Aristotle: The following adage is often attributed to him (put it into a search engine to see how many quotation websites have it): 'To write well, express yourself like the common people, but think like a wise man.' However, I cannot find an actual source for this and I suspect it's apocryphal. Nonetheless, I think the shear volume of Aristotle's writing speaks for itself. Moreover, Cicero wrote that 'if Plato’s prose was silver, Aristotle’s was a flowing river of gold'.
There is an argument against writing in Plato's Phaedrus, which, as this article points out, is perhaps ironic, seeing as it's in a written text. However, it may well simply be the case that Plato was, in this instance, faithfully reproducing Socrates' view on the subject, which would be consistent with the quotation from Cicero.
With the notable exceptions of Diogenes and Pyrrho, all major philosophers since Plato wrote their ideas down, although many if not most ancient texts are now lost. This is of course self-selecting though, since the ideas of a purely vocal philosopher are much less like to have come down through the centuries. (Jesus, whom some regard as a philosopher, is a big exception.)
You may wish to look up logocentrism, which, among other things, posits the primacy of speech over written text in the Western tradition.