Letters 40.14

And, I repeat, you could not attain it and at the same time preserve your sense of shame. Moreover, you would need to practise every day, and transfer your attention from subject matter to words. But words, even if they came to you readily and flowed without any exertion on your part, yet would have to be kept under control. For just as a less ostentatious gait becomes a philosopher, so does a restrained style of speech, far removed from boldness. Therefore, the ultimate kernel of my remarks is this: I bid you be slow of speech. Farewell.

Seneca, Letters to Lucilius 40.14, translated by Richard Mott Gummere